Ms. Barbie Nadeau’s book on the murder of Meredith Kercher is now out and will be reviewed here soon. A reading of some of her Newsweek and Daily Beast articles may give a glimpse of what to expect. Early in the article Ms. Nadeau wrote, “Just days after Kercher's body was found last November in the villa Knox shared with the victim, security camera footage showed the couple buying lingerie in a local store, with Knox giggling and telling Sollecito, ‘Afterwards I'm going to take you home so we can have wild sex together.’” Ms. Nadeau’s account is misleading in several respects. Ms. Knox did not have access to her own belongings at this time (her flat was a crime scene) and needed to buy underwear and borrow jeans. The security camera did not have sound, and witnesses say that the store has very loud music, making it difficult to overhear someone’s conversation. Whether the merchant, who was a paid interviewee and the actual source of the quote, spoke English or not is disputed. However, the couple did kiss in the store, and their demeanor appears playful.
Ms. Nadeau went on, “And by her own account in a prison diary leaked to the media, she details her sexual escapades with at least seven men she'd been with in her three months in Italy before her arrest. She even wrote that she might have HIV and then she uses a process of elimination to narrow down who might have given it to her. The diary is part of the collection of evidence and could be damaging to Knox in a court trial. Recently leaked segments of her continuing tome paint a disturbing picture of her state of mind. In one entry, she writes: ‘I think it's possible that Raffaelle went to Meredith's house, raped her, then killed her and then when he got home, while I was sleeping, he pressed my fingerprints n the knife.’”
Mark Waterbury rightly took Ms. Nadeau to task for the many problems with her assertions. Ms. Knox wrote of having seven intimate partners her whole life because she was told that she was or might be HIV-positive. Ms. Knox’s diary shows her emotional distress, and to claim that it “details her sexual escapades” is so blatantly wrong that it leaves one wondering what Ms. Nadeau could possibly have been thinking. Some of the most problematic assertions, including the incorrect description of the night of the murder, were based on an English translation of an Italian translation of her diary, instead of the original. When she was contacted about the mistranslation, Ms. Nadeau claimed that there was a second diary, but she is the only reporter who has made this claim to the best of my knowledge.
The last portion of the article says as much about Ms. Nadeau as about the case. “To complicate things further, Sollecito and Knox's reported break up prompted speculation that they would testify against each other. But Sollecito's flowers may be a signal that their defense teams may actually work together to pin the blame on Guede. If that strategy succeeds, the cipher of Amanda Knox may never truly be decoded.” Ms. Nadeau’s use of the word “pin” suggests that she believed Knox and Sollecito were guilty. Her linking the potential success of their blaming Mr. Guede to the potential failure to decipher Ms. Knox leaves little doubt about her opinion on their culpability. Why Newsweek entrusted their coverage of this case to her is the real mystery.
Let us consider some of her entries at The Daily Beast more briefly and with comments interspersed. In a recent article Nadeau wrote, “Shortly after her arrest, Knox admitted to being at the Perugian villa when Kercher was murdered. The confession was later thrown out of the body of evidence because of allegations of police brutality and coercion, but much of what she said in that original statement coincides with known elements of the case, including evidence gathered by CCTV footage from a nearby parking garage.” The CCTV footage may be of Meredith entering her cottage for the last time. Yet it is what this article does not say that is at least equally troubling. Nothing about the police giving out false information and only a little to on the British press, which sometimes behaved outrageously. Meredith’s father, John Kercher, was part of the British tabloid press corps, and this may explain some of the contempt the British press exhibited toward Ms. Knox.
Shortly after the conviction, Ms. Nadeau began an article, “Is the real Amanda Knox the sex-obsessed, cold-blooded murderer that the prosecution depicted? Or worse?” This question and the title of her article are truly egregious, worthy of comparison to the Newsweek mug shot cover on the Duke lacrosse case in 2006, and that is saying something. Clearly Ms. Nadeau had access to Edda Mellas and Curt Knox, which undercuts her claim about being shut out in the article about how the media got the case wrong (see above). The rest of the article lacks a critical appraisal of the forensics. “They [the jury] wondered why Amanda’s DNA and Meredith’s blood was wiped away and recovered with Luminol. They thought it was Raffaele’s bloody footprint on the bathroom rug and his DNA on Meredith’s bra clasp. They believed the prosecutor’s testimony that Meredith’s DNA was on the blade of the knife that had Amanda’s DNA on the handle.” There is no reason to assume that a substance that tests positive with Luminol is blood; it is a presumptive test that needs to be confirmed with one that is more specific for blood.
Immediately after the conviction Ms. Nadeau wrote, “At one point the stepmother of Raffaele Sollecito, Knox’s former boyfriend who was sentenced to 25 years for his part in the murder, yelled out ‘F@#k you,’” Ms. Nadeau is the only reporter who heard this; others heard, “Forte, Raffaele,” which just means strength, Raffaele. “But in the end, the two judges and six lay jurors trusted the sanctity of the DNA evidence, and doubted the words of Knox and Sollecito….For those who believed that Knox was guilty, the most damning evidence was the presence of her DNA mixed with Kercher’s blood in the house, and her statement that she was in the house at the time of the murder.” Ms. Nadeau has never written about the open letter signed by nine DNA forensics experts, but even if she is unaware of their views, she should know that the quality of the DNA evidence is very much in dispute.
Ms. Nadeau wrote about the jury’s report on its reasons for conviction, “A spot of Knox and Kercher’s mixed blood in one of the bedrooms, found using Luminol, and four additional spots in the small bathroom the girls shared also swayed the jurors.” The claim that finding Knox’s DNA mixed with Kercher’s blood means that their blood was mixed is dubious.
Quoting prosecutor Mignini Nadeau wrote, “’The window was broken from the inside, not the outside. The glass was on top of the clothes that had been strewn around the room, not under them. The break-in was staged and Knox is the one who did it.’ He also hinted that Knox and Sollecito might have been in a drug-fueled frenzy when they allegedly killed Kercher. He outlined the effects of cocaine and acid, and told the judges and jury how Knox and Sollecito ran with a crowd that often used these ‘stupificante,’ or stupefying drugs.” What drugs? Knox and Sollecito acknowledge smoking marijuana but no evidence of other drugs was presented. The notion that the window was broken from the inside is not convincing. Ms. Nadeau presents this closing argument without commenting on its many problems. This is only a reasonable approach if we accept this blog entry as pure reporting (with Ms. Nadeau reporting and editorializing are sometimes mixed. And yet after the introductory paragraph, eight of the nine succeeding paragraphs cover Mr. Mignini’s summation, whereas only one covers the defense’s summation.
“Other evidentiary problems include the lack of video or audio tapes of Knox’s original interrogation and the scientific police forgetting to pick up a bra clasp for nearly six weeks. That clasp is said to have Sollecito’s DNA on the metal hook and is the only material evidence police have tying Sollecito to the crime. While these obvious errors might well establish reasonable doubt in an American courtroom, it is unlikely they will have the same effect here in Italy, where defendants often seem to be presumed guilty until proven innocent.”
“Last July, testimony by noted forensic specialist Adriano Tagliabracci was abruptly suspended after the defense discovered that they had not been given all the prosecution’s evidence reports. Specifically, they did not have crucial evidence about Sollecito’s DNA found on the clasp of the bloodied bra that was cut from Kercher after she was stabbed.”
“Saturday’s hearing ended with a dramatic exchange about whether the prosecution had given the defense key documents regarding the DNA on Kercher’s bra. The charge was seen as a blatant attempt by the prosecution to throw the defense’s witness, and it worked. The exchange ended with Sollecito’s lawyers accusing the prosecution with illegality—a move many thought was primarily to set the stage for an appeal if one or both are convicted.” These three examples show that Ms. Nadeau does report on some aspects of the case that create sympathy for the defendants.
Ms. Nadeau wrote an article about Rudy Guede, who was the only person at that time convicted of Meredith Kercher’s murder. “’He has never changed his story,’ Guede’s lawyer, Valter Biscotti, told The Daily Beast this week. Biscotti would not supply any details about the version of events Guede gave at his own, closed-door trial, but he did say, ‘He has always maintained that they were all there, but that he is not the one who killed her.’” Ms. Nadeau did not comment on this remarkable assertion. When he was in Germany, the police intercepted one of Mr. Guede’s skype conversations in which he said that Amanda was not there. The first months after his arrest he said that an unidentified man murdered Ms. Kercher when Guede was on the toilet. Months later he began to claim that the man was Raffaele Sollecito and that Ms. Knox was at least present. ABC news reported that “Guede, 25, has at different times said the Knox, 22, of Seattle, was and was not at the house the night of the murder. At one point, he also implied that Knox's co-defendant Raffaele Sollecito was at the murder scene.”
Finally, I will expand upon a point I raised in the comments section of the previous article. In response to a question during a live chat, Ms. Nadeau said, “I think it is important to remember that the same scientific police and laboratories tested the DNA for all three suspects. That is to say, if the DNA matches Rudy and is accepted, then the DNA that matches the other two should also be accepted. How she may have left so little DNA if she was actually in the room is very hard to square.”
Ms. Nadeau is asserting implicitly that all DNA evidence is equal, but this is false. We know that the knife profile is weak, has drop-ins, and has considerable imbalance in intensity between most of the pairs of alleles. We know that the bra clasp was left in an insecure location for 47 days and handled poorly when it was finally collected. As Dan Krane said, “The science of DNA profiling is sound. But, not all of DNA profiling is science.” The evidence against Guede has never been released, and one cannot pass judgment on its quality without seeing it. There is second problem with Ms. Nadeau’s assertion. Rudy Guede was only identified as a suspect after the forensics came back, but Raffaele Sollecito and Amanda Knox were already suspects (first on the basis of demeanor, then on the basis of their interrogations) before the forensics was completed. This problem is particularly acute for the bra clasp, and one has to consider the problem of confirmation bias or even outright fraud when weighing the forensic evidence. The third problem is that even within a lab, the quality of work may not be uniform. For one thing lab contamination can be a sporadic event, as it was in the Jaidyn Leskie case. For another, there may be a lone sloppy or dishonest technician in a lab full of competent, ethical ones.
Update 20 April 2010
I added a hyperlink to the Newsweek story in paragraph 1 and the word "to" in paragraph 6, line 4.
Showing posts with label Rudy Guede. Show all posts
Showing posts with label Rudy Guede. Show all posts
Sunday, April 18, 2010
Monday, March 1, 2010
An interim evaluation of the evidence against Knox and Sollecito
Part IX in a series on the Knox/Sollecito case
Here is an interim overview of some of the evidence in the murder of Meredith Kercher; individual issues may be covered in greater depth once the reasons for the verdict have been announced. We have already examined some of the problems with the DNA of the knife and bra clasp. Problematic as the LCN DNA of the knife and the weak, mixed DNA of the clasp are, they are the only things that tie Mr. Sollecito to the room and Ms. Knox to a supposed murder weapon. Without them the whole case looks insubstantial.
Forensic evidence
The investigators failed to perform and especially to report the DNA forensics to the usual degree of completeness, and this leaves many questions unanswered. The investigators did not take Filomena’s or Laura’s reference DNA samples, even though they were Meredith’s roommates. Chris Mellas, Amanda’s stepfather, said that despite a court order in the summer of 2009, the investigators failed to disclose the electronic data files of the DNA evidence (called .fsa files) and logs to the defense. The lack of disclosure of evidence concerning the DNA forensics was one of the reasons that the defense essentially moved for a mistrial in the fall, a motion which was denied. According to Barbie Nadeau (http://www.thedailybeast.com/blogs-and-stories/2009-09-14/no-mistrial-for-knox/), “Just as court adjourned in July, it was revealed that the prosecution had held back key evidence from the defense and civil attorneys. On Monday, clutching the Italian constitution, Sollecito’s lead defense attorney, Giulia Bongiorno, told the judge: ‘My client has been denied his right to adequate representation.’”
Although Ms. Nadeau does not indicate the nature of the evidence withheld, the subsequent Johnson/Hampikian open letter of 19 November 2009 noted specifically lack of disclosure of the .fsa files. Because it is difficult to see why the defense would not share such files with Dr. Johnson and Professor Hampikian (or at least make them aware that the files had been finally disclosed), the open letter tends to corroborate Mr. Mellas’ account. In addition, Bob Graham wrote (http://www.dailymail.co.uk/news/article-1233539/Amanda-Knox-victim-anti-American-trial-campaigners-urge-Hillary-Clinton-launch-investigation.html), “Other forensic experts in several countries – including two from Britain – have started to study the DNA results but have delayed giving a verdict until they have received precise details on the methodology used by their Italian counterparts. The failure of the prosecution to provide these details to Knox and Sollecito’s defence teams is one of their central complaints.”
Why are the .fsa files important? Technical bulletin 40-035 from Chromosomal Laboratories, Inc., is a checklist of what the laboratory is expected to provide, and it states, “Copies of all data files used and created in the course of performing tests and analyzing data in this case, including .fsa files, if applicable. These files should include all data necessary to independently reanalyze the raw data.” In response to a question on this subject, Professor Dan Krane wrote, “The biggest concern that I personally have regarding this case is the refusal of the prosecution to provide the defense with a copy of the electronic data that underlies the DNA test results -- that is virtually unheard of world-wide today and it would be especially important to review that data in a case such as this which seems to involve such low level samples.” According to a knowledgeable source, “Each tested sample has its own file. The file contains the full electropherogram trace information along with other information about the testing conditions (e.g., date, time, injection time, voltage, temperature, current, the RFU threshold used by the analyst). If you have the electronic data, you can use the DNA analysis software (GeneScan & Genotyper or GeneMapper ID) to independently analyze the electronic data. That allows you to examine the results as closely as possible (zoom in on the electropherogram to evaluate low-level results) and establish the RFU threshold of your choosing.”
One leaves DNA by many mechanisms including shedding hair and skin. Finding Ms. Knox’s DNA in her own flat is a very unsurprising result, whether or not it happened to be mixed with Meredith’s blood. Her DNA was found in Mr. Sollecito’s flat as well. The lack of their DNA in Meredith’s room on all but the bra clasp is a silence that shouts. In a pretrial hearing, Mr. Sollecito’s lawyers argued that it would have been very unlikely for him to be able to leave DNA on the bra clasp without also leaving it on the bra as well, yet none was found there (http://www.telegraph.co.uk/news/3255101/DNA-on-Meredith-Kerchers-bloodied-bra-was-due-to-lab-contamination-claims-Sollecito.html).
The other biological forensics was also problematic. Luminol was overapplied to one of the footprints, according to Colonel Garofano in the book Darkness Descending, leading to a loss of detail in the image. Moreover, luminol is a presumptive test for blood, one that should be confirmed by further testing. Although some claim to have the ability to tell blood from other substances via luminol alone, this claim is controversial in the forensic literature. Moreover, defense expert witness Sara Gino stated "We were not told that, first of all, the prints were treated with a substance which should have indicated whether they were blood, and the result was very uncertain." In addition, the investigators did not obtain reference footprints from all of the roommates. The temperature of Meredith’s body was taken about two days after death had occurred, making it harder to estimate the time of death.
The investigators could have performed the electronic forensics much more professionally. For example, the investigators damaged three hard drives, Meredith’s, Amanda’s, and one of Raffale’s, (http://www.dailymail.co.uk/news/article-1234298/Amanda-Knox-The-troubling-doubts-Foxy-Knoxys-role-Meredith-Kerchers-murder.html). Amanda’s hard drive is said to have pictures of her and Meredith, evidence that would belie the impression that the two roommates did not get along, but her drive has not yet been salvaged. Her defense team has offered to pay for a different group of experts to attempt to retrieve the information, but this offer was rebuffed. The investigators also inadvertently erased a piece of potential alibi information (http://www.lastampa.it/redazione/cmsSezioni/cronache/200909articoli/47691girata.asp), the time that the file Stardust was accessed (http://perugia-shock.blogspot.com/2009/09/computer-places-knox-and-sollecito-at.html).
Non-forensic evidence
The prosecution would have us believe that a gang rape occurred, despite the fact that this is an unusual occurrence. Ms. Knox and Mr. Guede had met only twice, the two men had never met, and neither Ms. Knox nor Mr. Sollecito communicated with Mr. Guede in any documented way. It strikes me as extraordinarily risky to commit a crime with someone one does not know. Then Ms. Knox and Mr. Sollecito are imagined to have removed evidence linking them to the crime but not evidence linking Mr. Guede to the crime. In addition, the prosecution changed the motive during the trial but did not have evidence to support either motive.
Raffaele’s kitchen knife is too large to have made the bloody outline of the knife on the sheet. It is too large to make two of the three wounds, and any knife could have made the third. There is no reason for Raffaele and Amanda to have transported the knife in the first place. On top of that we are asked to believe that Raffaele and Amanda would not dispose of this knife, even though Rudy would have seen them use it and could rat them out, and even though the other knife was disposed of. We are also asked to believe that they would clean the blade of the knife but not the handle. This whole scenario would be risible if it were in a third-rate mystery novel.
Raffaele and Amanda are said to have faked evidence of the flat’s being burglarized. I do not find the argument that the break-in was staged to be convincing. There is little evidence pointing that way. Filomena’s room was tidy when she left it, but she recalled that when she returned, there was glass on her clothes. This suggests that someone put the clothes on the floor to simulate a break-in, then broke the window in her room. However, the photographic evidence is not definitive, and it is possible to imagine a number of explanations. Suppose the window were broken, and glass ended up on the laptop. Then suppose that the laptop were moved from the desk to the floor, where some of the glass slid off to some clothing and some remained on the computer. Also, Filomena was allowed back into her room to retrieve some items, and it is possible that she inadvertently did something to put glass on the strewn clothes and remembers the room as though she found it that way.
It has been argued that Raffaele called the Carabinieri after the unexpected arrival of the Postal Police, in an attempt to portray himself as a concerned but innocent citizen, then lied and said that his call to the Carabinieri preceded the appearance of the Postal Police (who were returning missing cell phones). The prosecution wants us to believe that Mr. Sollecito lied to the police about when he placed the call, before he was a suspect. The explanation for what probably did happen is complex, but unless one believes that Mr. Sollecito is very stupid, the prosecution’s theory does not make much sense. Attempting to lie about when the call to the Carabinieri would have little upside (he could have said to the postal police that he was just about to call them or the Carabinieri), and has a huge downside. One would generally believe that the police would be meticulous record keepers about the times of calls and other matters. If Mr. Sollecito were tempted to concoct this story, a moment’s thought should have been enough to convince him of the likelihood of being found out. The two defendants did do some dumb things, but I do not believe that they are that stupid.
Ms. Knox’s incriminating statements were thrown out as evidence for the murder trial; therefore, they cannot be used to assess her legal guilt or innocence. However, suppose we consider her incriminating statements against Lumumba in assessing factual innocence and ask why she made them. Her subsequent comments about the interrogation are similar to those made by people who have been pressured into making false confessions. Francesca Bene’s interrogation provides a modest amount of support for what Ms. Knox said, as discussed in a previous post. In addition, we have Douglas Preston’s account of his being interrogated in a foreign language, and his evaluation that his halting answers made him sound like a liar. It is quite possible that Ms. Knox’s interrogators misperceived similar behaviors of hers as evidence that she had something to hide and therefore pressed harder. Moreover, her later statement, “But I've said this many times so as to make myself clear: these things seem unreal to me, like a dream,” implicitly disavows Lumumba’s involvement.
The investigators claim that no undue coercion was used, but Dr. Giobbi said that he heard Amanda screaming. The investigators claim that they did not record the key interrogations with Amanda that night, despite having previously recorded her interviews and phone calls. Furthermore, they lied when they said that Amanda came in to the police headquarters of her own volition (http://perugia-shock.blogspot.com/2009/05/giobbi-i-gave-order.html). Therefore, Ms. Knox’s account of her interrogation is more credible than theirs is.
Ms. Knox’s allegedly performing a cartwheel at the police station was the fodder for a great deal of negative publicity. Her own explanation of that episode, as relayed through Chris Mellas to Frank Sfarzo of Perugia-Shock, is that she was stretching to relieve stress when a policeman commented on her flexibility. They fell into a conversation, and he asked her what other gymnastics or exercises she knew. Ms. Knox’s testimony at her trial mentioned meeting the policeman but did not say whether or not he asked her to demonstrate other gymnastic moves. Elsewhere, she implied that she did at least some exercises or stretches of her own accord. Therefore, her testimony neither contradicts nor confirms the version Mr. Sfarzo reported. In any case, her yoga or gymnastics have little or no bearing on her guilt or innocence.
What about Raffaele’s probable lie about his cooking with Meredith and his pricking her finger? Does this not generate suspicion? His statement was made only after he had heard that her DNA was found on the knife blade, not before, and it was made without knowledge of the quality of the data. His statement was stupid, but understandable. Therefore, I would say that there is reason to be suspicious of Amanda and Raffaele, probably not enough to indict, and certainly not enough to convict.
The defense have argued that this tragic crime was the work of a lone assailant, Rudy Guede. The evidence linking Mr. Guede to the crime is much stronger; there is a bloody handprint, the bowel movement in the toilet, and there are several pieces of DNA evidence. I am puzzled by the sexual aspect of the crime, but despite this reservation, Mr. Guede acting alone in the rape and murder is the most logical explanation to me. If information about Rudy’s involvement had come back earlier, I doubt that the investigators would have ever moved for an indictment against Raffaele or Amanda. In other words, this is an instance of garden-variety tunnel-vision on the part of the investigators.
Here is an interim overview of some of the evidence in the murder of Meredith Kercher; individual issues may be covered in greater depth once the reasons for the verdict have been announced. We have already examined some of the problems with the DNA of the knife and bra clasp. Problematic as the LCN DNA of the knife and the weak, mixed DNA of the clasp are, they are the only things that tie Mr. Sollecito to the room and Ms. Knox to a supposed murder weapon. Without them the whole case looks insubstantial.
Forensic evidence
The investigators failed to perform and especially to report the DNA forensics to the usual degree of completeness, and this leaves many questions unanswered. The investigators did not take Filomena’s or Laura’s reference DNA samples, even though they were Meredith’s roommates. Chris Mellas, Amanda’s stepfather, said that despite a court order in the summer of 2009, the investigators failed to disclose the electronic data files of the DNA evidence (called .fsa files) and logs to the defense. The lack of disclosure of evidence concerning the DNA forensics was one of the reasons that the defense essentially moved for a mistrial in the fall, a motion which was denied. According to Barbie Nadeau (http://www.thedailybeast.com/blogs-and-stories/2009-09-14/no-mistrial-for-knox/), “Just as court adjourned in July, it was revealed that the prosecution had held back key evidence from the defense and civil attorneys. On Monday, clutching the Italian constitution, Sollecito’s lead defense attorney, Giulia Bongiorno, told the judge: ‘My client has been denied his right to adequate representation.’”
Although Ms. Nadeau does not indicate the nature of the evidence withheld, the subsequent Johnson/Hampikian open letter of 19 November 2009 noted specifically lack of disclosure of the .fsa files. Because it is difficult to see why the defense would not share such files with Dr. Johnson and Professor Hampikian (or at least make them aware that the files had been finally disclosed), the open letter tends to corroborate Mr. Mellas’ account. In addition, Bob Graham wrote (http://www.dailymail.co.uk/news/article-1233539/Amanda-Knox-victim-anti-American-trial-campaigners-urge-Hillary-Clinton-launch-investigation.html), “Other forensic experts in several countries – including two from Britain – have started to study the DNA results but have delayed giving a verdict until they have received precise details on the methodology used by their Italian counterparts. The failure of the prosecution to provide these details to Knox and Sollecito’s defence teams is one of their central complaints.”
Why are the .fsa files important? Technical bulletin 40-035 from Chromosomal Laboratories, Inc., is a checklist of what the laboratory is expected to provide, and it states, “Copies of all data files used and created in the course of performing tests and analyzing data in this case, including .fsa files, if applicable. These files should include all data necessary to independently reanalyze the raw data.” In response to a question on this subject, Professor Dan Krane wrote, “The biggest concern that I personally have regarding this case is the refusal of the prosecution to provide the defense with a copy of the electronic data that underlies the DNA test results -- that is virtually unheard of world-wide today and it would be especially important to review that data in a case such as this which seems to involve such low level samples.” According to a knowledgeable source, “Each tested sample has its own file. The file contains the full electropherogram trace information along with other information about the testing conditions (e.g., date, time, injection time, voltage, temperature, current, the RFU threshold used by the analyst). If you have the electronic data, you can use the DNA analysis software (GeneScan & Genotyper or GeneMapper ID) to independently analyze the electronic data. That allows you to examine the results as closely as possible (zoom in on the electropherogram to evaluate low-level results) and establish the RFU threshold of your choosing.”
One leaves DNA by many mechanisms including shedding hair and skin. Finding Ms. Knox’s DNA in her own flat is a very unsurprising result, whether or not it happened to be mixed with Meredith’s blood. Her DNA was found in Mr. Sollecito’s flat as well. The lack of their DNA in Meredith’s room on all but the bra clasp is a silence that shouts. In a pretrial hearing, Mr. Sollecito’s lawyers argued that it would have been very unlikely for him to be able to leave DNA on the bra clasp without also leaving it on the bra as well, yet none was found there (http://www.telegraph.co.uk/news/3255101/DNA-on-Meredith-Kerchers-bloodied-bra-was-due-to-lab-contamination-claims-Sollecito.html).
The other biological forensics was also problematic. Luminol was overapplied to one of the footprints, according to Colonel Garofano in the book Darkness Descending, leading to a loss of detail in the image. Moreover, luminol is a presumptive test for blood, one that should be confirmed by further testing. Although some claim to have the ability to tell blood from other substances via luminol alone, this claim is controversial in the forensic literature. Moreover, defense expert witness Sara Gino stated "We were not told that, first of all, the prints were treated with a substance which should have indicated whether they were blood, and the result was very uncertain." In addition, the investigators did not obtain reference footprints from all of the roommates. The temperature of Meredith’s body was taken about two days after death had occurred, making it harder to estimate the time of death.
The investigators could have performed the electronic forensics much more professionally. For example, the investigators damaged three hard drives, Meredith’s, Amanda’s, and one of Raffale’s, (http://www.dailymail.co.uk/news/article-1234298/Amanda-Knox-The-troubling-doubts-Foxy-Knoxys-role-Meredith-Kerchers-murder.html). Amanda’s hard drive is said to have pictures of her and Meredith, evidence that would belie the impression that the two roommates did not get along, but her drive has not yet been salvaged. Her defense team has offered to pay for a different group of experts to attempt to retrieve the information, but this offer was rebuffed. The investigators also inadvertently erased a piece of potential alibi information (http://www.lastampa.it/redazione/cmsSezioni/cronache/200909articoli/47691girata.asp), the time that the file Stardust was accessed (http://perugia-shock.blogspot.com/2009/09/computer-places-knox-and-sollecito-at.html).
Non-forensic evidence
The prosecution would have us believe that a gang rape occurred, despite the fact that this is an unusual occurrence. Ms. Knox and Mr. Guede had met only twice, the two men had never met, and neither Ms. Knox nor Mr. Sollecito communicated with Mr. Guede in any documented way. It strikes me as extraordinarily risky to commit a crime with someone one does not know. Then Ms. Knox and Mr. Sollecito are imagined to have removed evidence linking them to the crime but not evidence linking Mr. Guede to the crime. In addition, the prosecution changed the motive during the trial but did not have evidence to support either motive.
Raffaele’s kitchen knife is too large to have made the bloody outline of the knife on the sheet. It is too large to make two of the three wounds, and any knife could have made the third. There is no reason for Raffaele and Amanda to have transported the knife in the first place. On top of that we are asked to believe that Raffaele and Amanda would not dispose of this knife, even though Rudy would have seen them use it and could rat them out, and even though the other knife was disposed of. We are also asked to believe that they would clean the blade of the knife but not the handle. This whole scenario would be risible if it were in a third-rate mystery novel.
Raffaele and Amanda are said to have faked evidence of the flat’s being burglarized. I do not find the argument that the break-in was staged to be convincing. There is little evidence pointing that way. Filomena’s room was tidy when she left it, but she recalled that when she returned, there was glass on her clothes. This suggests that someone put the clothes on the floor to simulate a break-in, then broke the window in her room. However, the photographic evidence is not definitive, and it is possible to imagine a number of explanations. Suppose the window were broken, and glass ended up on the laptop. Then suppose that the laptop were moved from the desk to the floor, where some of the glass slid off to some clothing and some remained on the computer. Also, Filomena was allowed back into her room to retrieve some items, and it is possible that she inadvertently did something to put glass on the strewn clothes and remembers the room as though she found it that way.
It has been argued that Raffaele called the Carabinieri after the unexpected arrival of the Postal Police, in an attempt to portray himself as a concerned but innocent citizen, then lied and said that his call to the Carabinieri preceded the appearance of the Postal Police (who were returning missing cell phones). The prosecution wants us to believe that Mr. Sollecito lied to the police about when he placed the call, before he was a suspect. The explanation for what probably did happen is complex, but unless one believes that Mr. Sollecito is very stupid, the prosecution’s theory does not make much sense. Attempting to lie about when the call to the Carabinieri would have little upside (he could have said to the postal police that he was just about to call them or the Carabinieri), and has a huge downside. One would generally believe that the police would be meticulous record keepers about the times of calls and other matters. If Mr. Sollecito were tempted to concoct this story, a moment’s thought should have been enough to convince him of the likelihood of being found out. The two defendants did do some dumb things, but I do not believe that they are that stupid.
Ms. Knox’s incriminating statements were thrown out as evidence for the murder trial; therefore, they cannot be used to assess her legal guilt or innocence. However, suppose we consider her incriminating statements against Lumumba in assessing factual innocence and ask why she made them. Her subsequent comments about the interrogation are similar to those made by people who have been pressured into making false confessions. Francesca Bene’s interrogation provides a modest amount of support for what Ms. Knox said, as discussed in a previous post. In addition, we have Douglas Preston’s account of his being interrogated in a foreign language, and his evaluation that his halting answers made him sound like a liar. It is quite possible that Ms. Knox’s interrogators misperceived similar behaviors of hers as evidence that she had something to hide and therefore pressed harder. Moreover, her later statement, “But I've said this many times so as to make myself clear: these things seem unreal to me, like a dream,” implicitly disavows Lumumba’s involvement.
The investigators claim that no undue coercion was used, but Dr. Giobbi said that he heard Amanda screaming. The investigators claim that they did not record the key interrogations with Amanda that night, despite having previously recorded her interviews and phone calls. Furthermore, they lied when they said that Amanda came in to the police headquarters of her own volition (http://perugia-shock.blogspot.com/2009/05/giobbi-i-gave-order.html). Therefore, Ms. Knox’s account of her interrogation is more credible than theirs is.
Ms. Knox’s allegedly performing a cartwheel at the police station was the fodder for a great deal of negative publicity. Her own explanation of that episode, as relayed through Chris Mellas to Frank Sfarzo of Perugia-Shock, is that she was stretching to relieve stress when a policeman commented on her flexibility. They fell into a conversation, and he asked her what other gymnastics or exercises she knew. Ms. Knox’s testimony at her trial mentioned meeting the policeman but did not say whether or not he asked her to demonstrate other gymnastic moves. Elsewhere, she implied that she did at least some exercises or stretches of her own accord. Therefore, her testimony neither contradicts nor confirms the version Mr. Sfarzo reported. In any case, her yoga or gymnastics have little or no bearing on her guilt or innocence.
What about Raffaele’s probable lie about his cooking with Meredith and his pricking her finger? Does this not generate suspicion? His statement was made only after he had heard that her DNA was found on the knife blade, not before, and it was made without knowledge of the quality of the data. His statement was stupid, but understandable. Therefore, I would say that there is reason to be suspicious of Amanda and Raffaele, probably not enough to indict, and certainly not enough to convict.
The defense have argued that this tragic crime was the work of a lone assailant, Rudy Guede. The evidence linking Mr. Guede to the crime is much stronger; there is a bloody handprint, the bowel movement in the toilet, and there are several pieces of DNA evidence. I am puzzled by the sexual aspect of the crime, but despite this reservation, Mr. Guede acting alone in the rape and murder is the most logical explanation to me. If information about Rudy’s involvement had come back earlier, I doubt that the investigators would have ever moved for an indictment against Raffaele or Amanda. In other words, this is an instance of garden-variety tunnel-vision on the part of the investigators.
Sunday, January 3, 2010
Amanda Knox and Raffaele Sollecito and the murder of Meredith Kercher, Part I
Introduction to the case
This post will be the first in a series of articles on the Amanda Knox/Raffaele Sollecito case. Amanda Knox is an American student, and Italian Raffaele Sollecito is her former boyfriend. Both of these two individuals were convicted of the murder of British student Meredith Kercher in late 2009. Rudy Guede was previously convicted of her murder in a separate, fast-track trial in 2008. Many in the United States have criticized the prosecutor’s summation (http://blog.simplejustice.us/2009/12/05/a-trial-without-evidence.aspx) and the forensics (http://www.sciencespheres.com/2009/10/methods-of-polizia-pseudoscientificaa.html).
The DNA forensics in this case centers around two items, Meredith Kercher’s bra clasp and Raffale Sollecito’s kitchen knife. This article will focus on some of the issues surrounding the knife. The kitchen knife had Amanda’s DNA on the handle, which is not surprising given that Amanda cooked at Raffaele’s house. But the prosecution claims that their forensics investigators found a small amount of Meredith’s DNA on the blade. This claim is dubious at best, but even if it were true, the knife cannot be the sole murder weapon. Let’s take up the second question first.
Problems with the knife
First, Mr. Sollecito’s kitchen knife was too large to have made two of the three wounds on Ms. Kercher’s body. The smaller knife, the one that made the first two wounds, may have also made the third wound. Second, the kitchen knife does not match the bloody outline of a knife at the crime scene (http://www.newsweek.com/id/216903/page/2). Third, Newsweek reported that, “an officer testifying at the trial said he used ‘police intuition’ when choosing that knife from Sollecito's cutlery.” If there were multiple knives in the drawer, why choose one that had a different outline from the one whose outline was on Ms. Kercher’s sheets? The claim of police intuition does not make any sense.
But possibly the most serious reason for doubting that DNA was really on the knife is that it tested negative for blood (http://www.sciencespheres.com/2009/12/why-knife-was-not-knife.html. Dr. Stefanoni opined that the knife had been cleaned with bleach. This is a puzzling claim even at the outset, because bleach does not leave a corrosive mark on stainless steel; however, the prosecution’s argument becomes even more questionable upon further inspection. Drs. Elizabeth A. Johnson and Greg Hampikian, both experts in DNA forensics, coauthored an open letter about some of the evidence in this case (http://www.friendsofamanda.org/articles.html). About the cleaning of the knife, they said:
This DNA does not originate from blood. A highly sensitive chemical test for blood was negative, and it is unlikely that all chemically detectable traces of blood could be removed while retaining sufficient cells to produce a DNA profile consistent with the victim.
Indeed, bleach is so effective at destroying DNA that it is used in research laboratories for that very purpose (A. M. Prince, L. Andrus PCR: How to kill unwanted DNA, Biotechniques, Vol. 12, No. 3, 358-360). It far more effective than acid! Bleach is also used in some anthropological work to destroy unwanted DNA on the surface of an object that would contaminate valuable DNA inside. The very fact that there was no blood on the knife suggests that there was also no DNA on the knife; therefore, contaminating DNA is the most likely source for the signals that were observed. These three reasons call into question whether the kitchen knife had anything to do with the murder.
What the laboratory of Dr. Patrizia Stefanoni should have done is to save some of the material for a retest. As mentioned previously, this lab should have tested other knives, and perhaps other, random implements, in Raffele Sollecito’s drawer in the same way. Would DNA have also shown up on a different knife? These control experiments would have clarified whether Meredith Kercher’s DNA was really on the knife or not. However, we can at least examine the data that were produced from the knife.
Introduction to DNA forensics
Modern DNA forensic analysis (birg.cs.wright.edu/talks/Human Identification 2008.ppt) produces fluorescent signals that must be observed and interpreted properly to exclude or not exclude a person as a DNA contributor. The fluorescent signals arise from a collection of DNA molecules of various lengths (sizes) that are produced by chopping the DNA strands at a set of specific locations, and then separated using capillary electrophoresis. The pattern of signals from the DNA form what is called an electropherogram. The electropherogram from a piece of evidence is compared against reference samples from various individuals.
Fluorescence Spectroscopy
Spectroscopy is the study of how light interacts with matter. All spectroscopic experiments involve the observation of photons of light above a background of random noise. All forms of spectroscopy must contend with the fact that signal-to-noise (S/N) ratios are not infinite. The S/N ratio is a measure of the strength of the signal and is often related to the concentration of the chemical species that produces it. DNA forensics makes use of chemical labels that produce fluorescence. In a DNA electropherogram the S/N ratio is measured in relative fluorescence units (RFUs). Why are S/N ratios so important in regards to the DNA sample on the knife blade in the Amanda Knox/Raffaele Sollicito case?
The open letter coauthored by Dr. Elizabeth and Professor Gregory Hampikian and cosigned by several others had this to say about the knife DNA:
An extremely low level, partial DNA profile was developed for the blade swabbing using the Identifiler kit. The alleles detected were consistent with the DNA of the victim. The highest peak in the electropherogram was approximately 100 relative fluorescence units (rfu), while 21 of the 29 peaks that were detected and labeled as alleles fell between 20 and 50 rfu….No credible scientific evidence has been presented to associate this kitchen knife with the murder of Meredith Kercher. (emphasis added)
Signal-to-Noise Ratios
To understand their conclusion we need to know more about signals and noise. Suppose you are driving your car away from your home town and you have tuned in your favorite FM radio station. As you travel farther away, the music gets fainter (the signal is now weaker), so you turn up the gain (amplification). Now the music is more audible, but you start to hear crackles (the noise). Amplification affects both signal and noise. Eventually, you will travel so far away that the noise becomes more unpleasant and you switch to a different station (the S/N ratio has become unacceptably low).
Now let us ask what would happen if you were 200 miles away and you tuned to the frequency of your favorite FM station in your home city. You would hear nothing but noise, sometimes called static. Based only on your observation, you could not say that the station was even broadcasting. It is not that you would deny that the station was broadcasting, it is just that you cannot affirm it on the basis of your observation; your observation is indeterminate.
Each DNA forensic laboratory establishes a threshold value for the size of acceptable peaks, but the threshold values are not identical from lab-to-lab. Setting a minimum threshold does not automatically favor the defense or the prosecution. The lowest such value of which I am aware is 40 (http://www.bioforensics.com/articles/champion1/champion1.html). At first this seems large, since peaks smaller than this are still greater than noise, but these peaks are small relative to those typically encountered in DNA electropherograms.
Instead of examining the specific choice of a threshold value, let us discuss why setting them in advance of the experiment is so important. Scientists set up their experiments to test (falsify) their hypotheses. If the signal-to-noise level in any spectroscopic experiment falls below the threshold, any hypothesis requiring that the signal be above the threshold must be rejected. The reason one sets the threshold first is to avoid bias. The textbook An Introduction to Forensic DNA analysis, 2nd ed. (Rudin, N. and Inman, K., CRC Press 2002, p. 121) states (emphasis added), “It is important to have some predetermined limit to distinguish what is signal and what is noise.” If one treats the threshold as flexible, the very purpose for setting it prior to running the experiment is defeated.
How does this relate to the DNA electropherogram of the knife sample (http://www.friendsofamanda.org/articles.html, Figure 1)? 16 out of 29 peaks are lower than 40 in S/N, and 22 are lower than 50 RFU. Dr. Stefanoni herself wrote (http://www.thedailybeast.com/blogs-and-stories/2009-09-14/no-mistrial-for-knox/) the words “too low” with respect to the knife. In other words these peaks are too small to count as music in the car radio analogy above.
It would be helpful to know the threshold value regularly employed in Dr. Stefanoni’s lab, but it could have been as high as 150 RFU and is very unlikely to be below 40 RFU. The signals above the threshold might constitute a partial profile of Ms. Kercher’s DNA. However, such a partial match is very problematic (http://www.scientific.org/tutorials/articles/riley/riley.html):
1. A partial profile essentially proves that one is operating outside of well-characterized and recommended limits.
2. Contaminating DNA usually presents as a partial profile, although not always. For this reason, the risk that the result is a contaminant is greater than for samples that present as full profiles.
3. A partial profile is at risk of being incomplete and misleading. The partial nature of it proves that DNA molecules have been missed. There is no way of firmly determining what the complete profile would have been, except by seeking other samples that may present a full profile.
Conclusions
The kitchen knife cannot be the sole murder weapon, and it most likely had nothing to do with the crime whatsoever. The only evidence that it might have played any role is the finding of DNA that is at best a partial match to Ms. Kercher’s DNA on the blade, and that almost certainly came from contamination during the test. Given the weakness of the fluorescence signals and especially the lack of blood on the knife, the signals observed do not tie the knife to the crime. No wonder that the open letter quoted above ends its section on the kitchen knife by concluding that there is no forensic evidence to link it to the crime. But an equally troubling problem with the prosecution’s theory is that Ms. Knox and Mr. Sollecito would bother to take this knife from his flat to the dwelling occupied by Ms. Knox, Ms. Kercher, and their two roommates in preference to using knives found in the kitchen of these four roommates. What sense does that make? It is typical of this case that Occam’s razor is so often ignored.
Update, 01/18/2010
The prosecuation's theory would also have us believe that Knox would not dispose of the supposed murder weapon, and despite cleaning the blade extensively, would not clean her fingerprints from the handle. This strikes me as unlikely.
This post will be the first in a series of articles on the Amanda Knox/Raffaele Sollecito case. Amanda Knox is an American student, and Italian Raffaele Sollecito is her former boyfriend. Both of these two individuals were convicted of the murder of British student Meredith Kercher in late 2009. Rudy Guede was previously convicted of her murder in a separate, fast-track trial in 2008. Many in the United States have criticized the prosecutor’s summation (http://blog.simplejustice.us/2009/12/05/a-trial-without-evidence.aspx) and the forensics (http://www.sciencespheres.com/2009/10/methods-of-polizia-pseudoscientificaa.html).
The DNA forensics in this case centers around two items, Meredith Kercher’s bra clasp and Raffale Sollecito’s kitchen knife. This article will focus on some of the issues surrounding the knife. The kitchen knife had Amanda’s DNA on the handle, which is not surprising given that Amanda cooked at Raffaele’s house. But the prosecution claims that their forensics investigators found a small amount of Meredith’s DNA on the blade. This claim is dubious at best, but even if it were true, the knife cannot be the sole murder weapon. Let’s take up the second question first.
Problems with the knife
First, Mr. Sollecito’s kitchen knife was too large to have made two of the three wounds on Ms. Kercher’s body. The smaller knife, the one that made the first two wounds, may have also made the third wound. Second, the kitchen knife does not match the bloody outline of a knife at the crime scene (http://www.newsweek.com/id/216903/page/2). Third, Newsweek reported that, “an officer testifying at the trial said he used ‘police intuition’ when choosing that knife from Sollecito's cutlery.” If there were multiple knives in the drawer, why choose one that had a different outline from the one whose outline was on Ms. Kercher’s sheets? The claim of police intuition does not make any sense.
But possibly the most serious reason for doubting that DNA was really on the knife is that it tested negative for blood (http://www.sciencespheres.com/2009/12/why-knife-was-not-knife.html. Dr. Stefanoni opined that the knife had been cleaned with bleach. This is a puzzling claim even at the outset, because bleach does not leave a corrosive mark on stainless steel; however, the prosecution’s argument becomes even more questionable upon further inspection. Drs. Elizabeth A. Johnson and Greg Hampikian, both experts in DNA forensics, coauthored an open letter about some of the evidence in this case (http://www.friendsofamanda.org/articles.html). About the cleaning of the knife, they said:
This DNA does not originate from blood. A highly sensitive chemical test for blood was negative, and it is unlikely that all chemically detectable traces of blood could be removed while retaining sufficient cells to produce a DNA profile consistent with the victim.
Indeed, bleach is so effective at destroying DNA that it is used in research laboratories for that very purpose (A. M. Prince, L. Andrus PCR: How to kill unwanted DNA, Biotechniques, Vol. 12, No. 3, 358-360). It far more effective than acid! Bleach is also used in some anthropological work to destroy unwanted DNA on the surface of an object that would contaminate valuable DNA inside. The very fact that there was no blood on the knife suggests that there was also no DNA on the knife; therefore, contaminating DNA is the most likely source for the signals that were observed. These three reasons call into question whether the kitchen knife had anything to do with the murder.
What the laboratory of Dr. Patrizia Stefanoni should have done is to save some of the material for a retest. As mentioned previously, this lab should have tested other knives, and perhaps other, random implements, in Raffele Sollecito’s drawer in the same way. Would DNA have also shown up on a different knife? These control experiments would have clarified whether Meredith Kercher’s DNA was really on the knife or not. However, we can at least examine the data that were produced from the knife.
Introduction to DNA forensics
Modern DNA forensic analysis (birg.cs.wright.edu/talks/Human Identification 2008.ppt) produces fluorescent signals that must be observed and interpreted properly to exclude or not exclude a person as a DNA contributor. The fluorescent signals arise from a collection of DNA molecules of various lengths (sizes) that are produced by chopping the DNA strands at a set of specific locations, and then separated using capillary electrophoresis. The pattern of signals from the DNA form what is called an electropherogram. The electropherogram from a piece of evidence is compared against reference samples from various individuals.
Fluorescence Spectroscopy
Spectroscopy is the study of how light interacts with matter. All spectroscopic experiments involve the observation of photons of light above a background of random noise. All forms of spectroscopy must contend with the fact that signal-to-noise (S/N) ratios are not infinite. The S/N ratio is a measure of the strength of the signal and is often related to the concentration of the chemical species that produces it. DNA forensics makes use of chemical labels that produce fluorescence. In a DNA electropherogram the S/N ratio is measured in relative fluorescence units (RFUs). Why are S/N ratios so important in regards to the DNA sample on the knife blade in the Amanda Knox/Raffaele Sollicito case?
The open letter coauthored by Dr. Elizabeth and Professor Gregory Hampikian and cosigned by several others had this to say about the knife DNA:
An extremely low level, partial DNA profile was developed for the blade swabbing using the Identifiler kit. The alleles detected were consistent with the DNA of the victim. The highest peak in the electropherogram was approximately 100 relative fluorescence units (rfu), while 21 of the 29 peaks that were detected and labeled as alleles fell between 20 and 50 rfu….No credible scientific evidence has been presented to associate this kitchen knife with the murder of Meredith Kercher. (emphasis added)
Signal-to-Noise Ratios
To understand their conclusion we need to know more about signals and noise. Suppose you are driving your car away from your home town and you have tuned in your favorite FM radio station. As you travel farther away, the music gets fainter (the signal is now weaker), so you turn up the gain (amplification). Now the music is more audible, but you start to hear crackles (the noise). Amplification affects both signal and noise. Eventually, you will travel so far away that the noise becomes more unpleasant and you switch to a different station (the S/N ratio has become unacceptably low).
Now let us ask what would happen if you were 200 miles away and you tuned to the frequency of your favorite FM station in your home city. You would hear nothing but noise, sometimes called static. Based only on your observation, you could not say that the station was even broadcasting. It is not that you would deny that the station was broadcasting, it is just that you cannot affirm it on the basis of your observation; your observation is indeterminate.
Each DNA forensic laboratory establishes a threshold value for the size of acceptable peaks, but the threshold values are not identical from lab-to-lab. Setting a minimum threshold does not automatically favor the defense or the prosecution. The lowest such value of which I am aware is 40 (http://www.bioforensics.com/articles/champion1/champion1.html). At first this seems large, since peaks smaller than this are still greater than noise, but these peaks are small relative to those typically encountered in DNA electropherograms.
Instead of examining the specific choice of a threshold value, let us discuss why setting them in advance of the experiment is so important. Scientists set up their experiments to test (falsify) their hypotheses. If the signal-to-noise level in any spectroscopic experiment falls below the threshold, any hypothesis requiring that the signal be above the threshold must be rejected. The reason one sets the threshold first is to avoid bias. The textbook An Introduction to Forensic DNA analysis, 2nd ed. (Rudin, N. and Inman, K., CRC Press 2002, p. 121) states (emphasis added), “It is important to have some predetermined limit to distinguish what is signal and what is noise.” If one treats the threshold as flexible, the very purpose for setting it prior to running the experiment is defeated.
How does this relate to the DNA electropherogram of the knife sample (http://www.friendsofamanda.org/articles.html, Figure 1)? 16 out of 29 peaks are lower than 40 in S/N, and 22 are lower than 50 RFU. Dr. Stefanoni herself wrote (http://www.thedailybeast.com/blogs-and-stories/2009-09-14/no-mistrial-for-knox/) the words “too low” with respect to the knife. In other words these peaks are too small to count as music in the car radio analogy above.
It would be helpful to know the threshold value regularly employed in Dr. Stefanoni’s lab, but it could have been as high as 150 RFU and is very unlikely to be below 40 RFU. The signals above the threshold might constitute a partial profile of Ms. Kercher’s DNA. However, such a partial match is very problematic (http://www.scientific.org/tutorials/articles/riley/riley.html):
1. A partial profile essentially proves that one is operating outside of well-characterized and recommended limits.
2. Contaminating DNA usually presents as a partial profile, although not always. For this reason, the risk that the result is a contaminant is greater than for samples that present as full profiles.
3. A partial profile is at risk of being incomplete and misleading. The partial nature of it proves that DNA molecules have been missed. There is no way of firmly determining what the complete profile would have been, except by seeking other samples that may present a full profile.
Conclusions
The kitchen knife cannot be the sole murder weapon, and it most likely had nothing to do with the crime whatsoever. The only evidence that it might have played any role is the finding of DNA that is at best a partial match to Ms. Kercher’s DNA on the blade, and that almost certainly came from contamination during the test. Given the weakness of the fluorescence signals and especially the lack of blood on the knife, the signals observed do not tie the knife to the crime. No wonder that the open letter quoted above ends its section on the kitchen knife by concluding that there is no forensic evidence to link it to the crime. But an equally troubling problem with the prosecution’s theory is that Ms. Knox and Mr. Sollecito would bother to take this knife from his flat to the dwelling occupied by Ms. Knox, Ms. Kercher, and their two roommates in preference to using knives found in the kitchen of these four roommates. What sense does that make? It is typical of this case that Occam’s razor is so often ignored.
Update, 01/18/2010
The prosecuation's theory would also have us believe that Knox would not dispose of the supposed murder weapon, and despite cleaning the blade extensively, would not clean her fingerprints from the handle. This strikes me as unlikely.
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