Gary Leiterman and DNA contamination

Jane Mixer was initially thought to be the victim of a possible serial killer, John Norman Collins.  Jane Mixer was murdered in 1969 near Ann Arbor, MI, but the DNA testing was done until 2002, a gap of approximately 33 years.  One item of evidence from the Mixer case showed DNA from John Ruelas, and several locations (on some panty hose and a towel) showed DNA from Gary Leiterman.  Despite the fact that the state had no other evidence against Leiterman, he was convicted of her murder in 2005.  John Ruelas was never charged.

A drop of blood from Mixer’s hand was preserved, and DNA from John Ruelas was found.  The prosecutor believed that the blood was from John Ruelas, but he did not offer a satisfactory explanation of how his blood came to be there.  Because Ruelas was four years old at the time of the murder and lived about forty miles away, the possibility that his DNA arrived instead via contamination must be considered.  As defense expert witness Theodore Kessis wrote, “The unexpected and never accounted for finding of John Ruelas’ profile on evidence in the Mixer case clearly demonstrates the proposition that contamination can and does occur between samples from different cases.”

The presence of Ruelas’ DNA is most easily explained by the fact that samples from John Ruelas were also processed in the crime laboratory of the State Police of Michigan contemporaneously with the samples from the Mixer murder.  But can the absence of Mixer’s DNA in the blood drop also be explained?  In 2004 C. Peel and P. Gill (“Attribution of DNA profiles to body fluid stains,” International Congress Series 1261, pp. 53-55) performed a series of experiments, in which a good DNA shedder handled the substrate (cotton or glass) for a blood stain, either before or after the blood from a different individual was placed on the substrate.  The blood was either diluted or the stain had been left to sit for some months, allowing for possible DNA degradation over time.  They used leucomalachite green as a presumptive test for blood.  Peel and Gill wrote, “…the more dilute or degraded the stain, the higher the contribution of the substrate handler’s DNA to the resulting profile.  A positive presumptive test could be obtained from samples when a profile originating from the body fluid was no longer detectable.”  Although it is tempting to associate the DNA that one finds in a stain to that stain, such an association is occasionally in error.  In some cases substrate controls can be helpful in determining whether or not DNA is associated with a particular stain.

It is essentially 100% certain that Ruelas’s DNA arrived on the items from the Mixer case via contamination, although the exact route is unclear.   Gary Leiterman’s DNA was also in the laboratory at that time.  No body fluid could be associated with Leiterman’s DNA associated with evidence from the Mixer case.  Sub-source DNA such as this is weaker in probative value than DNA associated with a particular tissue or body fluid.  Taking these facts and ideas into consideration, Leiterman’s DNA probably also arrived via contamination. 

A second line of evidence also implies that contamination is the most likely explanation.  A lab worker performed a negative control experiment during the time that a sample from the panty hose was being tested.  The negative controls will only show the presence of DNA in an electropherogram if DNA has been introduced unexpectedly into the experiment.  Theodore Kessis wrote, “Review of the electropherograms associated with this negative control sample (NEG 041902) reveals that it was contaminated, a fact that cannot be disputed since Dr. Milligan himself labeled it with a note indicated as much (Appendix 8 – Electropherogram sample NEG 041902).  Remarkably, Dr. Milligan stated in his 7/15/02 testimony that no contamination events had occurred during the course of his testing and that if any had, he would have documented them in his reporters (p. 141-21 and 142-4).  Equally difficult to rectify here is the fact that when asked if he had ever committed an error, Dr. Milligan’s replied that he could never recall making one.”  CBS News reported that, “Lab supervisor Jeffrey Nye says he retraced every step and he does not believe there is any issue of contamination. ‘No issue whatsoever,’ he says.”  This is an astonishing statement.

This lack of disclosure of a contamination event and a similar occurrence in the Adam Scott case (Peter Gill, Misleading DNA Evidence, Academic Press, 2014, p. 22) demonstrates that one cannot implicitly rely upon a laboratory to report accurately the results of negative control reactions.  Yet this is valuable information; a jury might choose to discount testimony from a lab if it knew contamination had happened.  It is also worth recalling what William Thompson noted in “Tarnish on the Gold Standard,” which is that the some laboratory workers tamper with negative controls in various ways.  For these reasons full disclosure of the negative controls in the form of raw (meaning unprocessed) data is the best course of action for a judicial system.  Students of the Knox/Sollecito case will not be surprised to learn that the position of the Michigan State Police crime laboratory was foursquare against disclosure of the raw data.  Professor Thompson wrote, “The Deputy Director of the Michigan State Police issued a statement on May 12, 2005 opposing ‘the allowance of releasing raw electronic data for subsequent manipulations using software and parameters not validated by the Michigan State Police Forensic Laboratory’ and declaring that ‘it is the position of the Michigan State Police Forensic Science Division that any release of this (sic) data for processing with non-validated parameters is tantamount to evidence tampering.’”²⁶  This is a self-evidently nonsensical position, and it also forces one to ask why the processing parameters chosen by a forensic laboratory are necessarily the optimal ones.

Conclusions

The DNA evidence against Gary Leiterman is compromised so completely by the presence of the DNA from John Ruelas that it scarcely should be called evidence at all.  Exactly how their DNA came to be on items of evidence from the murder of Jane Mixer is not known.  Dr. Theodore Kessis commented on the Benjamin LaGuer case:  “It is highly improbable that any given forensic DNA laboratory will take it upon itself to contact its accrediting bodies or the press and state for the record how often they make mistakes… To best understand the weaknesses associated with DNA testing we must rely upon the empirical, the occasions in which such deficiencies are revealed either by the press or internal review of a lab’s documentation of such problems by a defense expert.  A close look at either reveals that indeed many instances of DNA testing errors have lead to the false conviction of individuals.”  Regrettably, even the sworn testimony of laboratory personnel may be seriously in error, as in the Leiterman case.  Nor can a jury be counted upon to accurately weigh the odds of contamination.    Quite the contrary, juries sometimes discount alibi evidence, such as the Farah Jama case, or the fact that the defendant lived in one city and claimed never having been to the city where the crime occurred, as happened in the Adam Scott case.  Both cases are now generally believed to be instances of DNA contamination.

Unresolved issues in the latest round of DNA testing in the Hank Skinner case

DNA testing in the Hank Skinner case began again in 2012 after the state of Texas dropped its objections after a fight that lasted over a decade.  After the release of some preliminary data, the prosecution declared that it confirmed Skinner’s guilt, as reported by Jordan Smith in the Austin Chronicle.  Mr. Skinner’s attorney issued a response stating that not all testing was complete and that defense experts had not had a chance to examine the results yet.  Skinner had been found guilty of murdering his live-in girlfriend Twila Busby and her two grown sons.  He claims that he is innocent, and there is an alternate suspect in this case, Robert Donnell, who was Twila’s uncle.

Mr. Skinner’s DNA was found on 10 of 40 items tested.  Many of the items tested appear to have been blood, and they come from various locations around the house.  There are profiles that belong to an unknown individual or individuals, including one unknown profile on a knife that has DNA deposited by Mr. Skinner and by Elwin Caler, one of Ms. Busby’s sons.  There is also an unknown profile from a bloodstain in the sons’ bedroom.  The unknown profiles may not be complete, but that is one of several issues that further testing might resolve.

My conclusions at this time are that the advisory paints an incomplete (therefore misleading) picture of the case and is overinterpreting both the previous DNA results and the present ones.  For example, the prosecution’s advisory summarized the testimony of a witness who claimed that Mr. Skinner threatened her, but the witness later recanted, a fact that was ignored.  The advisory failed to mention anything about two bloody handprints and bloody bootprints that have been discussed in one report on this case. "The State tested the bloody handprints against those of Hank Skinner.  Hank was good for the three handprints near the back of the house.  The handprint on the trash bag, and presumably the handprint on the front storm door, belonged to someone else." The existence of the jacket, the handprints that apparently do not match, and the bloody bootprints that are not his size are some of the objections to the prosecution's case.

With respect to DNA profiling the first problem is that the most compelling piece of exculpatory evidence, what one person identified as Donnell’s jacket, has been lost before it could be tested.  The jacket is stained with blood and sweat.  If either Donnell’s DNA were found on the jacket or if some of the blood were Twila’s), that would establish reasonable doubt, at the very least.  However, at present there is no reference profile of Robert Donnell (see also below).  The failure to obtain his profile could be a consequence of the investigatory tunnel vision that has plagued this case, as a previous entry here indicated.  I suggest that the State of Texas exhume his body or obtain his DNA in some other way.

A second problem centers around whether Twila was sexually assaulted on the night of her death.  The vaginal DNA profiling was performed by standard autosomal DNA methods, in which DNA deposited by a possible perpetrator can become overwhelmed by the victim’s own DNA.  There is nothing in the public record of Y-STR testing being performed, despite its routine use in sexual assaults.  The unique advantage of Y-STR profiling is that it involves only the Y chromosome, which women do not have; therefore, a male contribution to a mixture can be selectively amplified by the polymerase chain reaction.  Either the laboratory did not do Y-STR testing, or it did but the results were not included in the advisory.  In addition the fingernail clippings either showed Ms. Busby’s DNA, or they did not show any DNA.  Moreover, fingernail scrapings can also be tested with Y-STR forensics, which has marginally higher sensitivity than autosomal testing.  Mr. Skinner’s attorney indicated that the defense has requested additional testing; therefore, it is possible that Y-STR results will be forthcoming.

A third problem concerns the existence of DNA from at least one unknown person.  The evidence with respect to the knife appears inculpatory at first glance, yet it is undisputed that Mr. Skinner was bleeding that night.  It is likely that his contribution to the knife DNA profile arose from his blood, and one obvious possibility is that he cut himself while committing the murders. The defense should raise two alternate hypotheses.  There is chance that his profile arose from casual use of this knife around the house prior to the murder.  In addition, Mr. Skinner was incoherent according to one witness due to a combination of alcohol and codeine; therefore, his DNA could have been deposited by his possibly handling the knife at some point after the murder when he was allegedly stumbling around the house.  It is also undisputed that he was in close proximity to the victims that night; therefore, positing that he handled the knife, although speculative, is not unreasonable. 

The Skeptical Juror wrote, "Fresh blood drops were found on the sidewalk, near the front door of the house where the murders took place.  Those drops were tested.  The DNA from those drops belonged not to Hank Skinner, but to an unidentified male." The most recent DNA profiling also did not test the gauze, even though it may have been used to wipe the knife, which is odd.  I wonder whether this profile was similar to or different from the ones turned up in the most recent round of testing, and I also wonder who the DNA donor(s) is(are).  The former question might be addressed by treating the DNA from the blood drops on the sidewalk as something like a reference profile.  DNA mixtures are sometimes deconvoluted by a process known as sequential unmasking, in which a forensic worker is given information about the reference profiles in a gradual manner, only after completing a relevant portion of the analysis.  Yet even the mere existence of blood from another person calls for an explanation.  Was the blood fresh?  If so, who was bleeding besides Mr. Skinner, Ms. Busby, Mr. Caler, and Mr. Randy Busby, Twila’s other son (all of whose reference profiles are available)?

Finally, a fourth problem is that one of the samples may have been contaminated with some DNA from a laboratory worker.  This kind of event actually happens not infrequently in DNA profiling, but it does mean that the defense needs to scrutinize the negative controls and machine logs to look for other evidence of contamination.  Negative controls will detect large scale contamination that affects multiple items of evidence, but will often not detect sporadic contamination affecting a single sample, as Professor William Thompson has pointed out:  “However, the same processes that cause detectable errors in some cases can cause undetectable errors in others. If DNA from a suspect is accidentally transferred into a ‘blank’ control sample, it is obvious that something is wrong; if the suspect’s DNA is accidentally transferred into an evidentiary sample, the error is not obvious because there is another explanation — i.e., that the suspect is the source of the evidentiary DNA.”

One hopes and expects that future rounds of DNA testing will address some of these shortcomings.  Both the victims’ families and Hank Skinner deserve nothing less than a full accounting of what happened that terrible night.  However, the prosecutor brings charges in the name of the people; therefore, every citizen has some responsibility for what happens in a courtroom, including the times when there is a miscarriage of justice.