Tuesday, December 2, 2014
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.
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.