Fortunately, people in general seem to have gotten the message about the issues with memory. Unfortunately, they tend to put too much faith in other types of evidence, which can be just as fallible.
DNA evidence is viewed by many as the gold standard in forensic evidence. But just as there is a right and wrong way to obtain eyewitness evidence, there are strict processes that must be followed in examining DNA evidence, or you run the risk of invalidation.
An article in the APS Observer discusses a cold case that was "solved" with DNA evidence. However, the story needed to explain that evidence is convoluted, and the possibility that the DNA evidence was contaminated seems much more likely. APS Fellow John Wixted explains:
As part of the “Psychology & Law” class that I teach, I set out to illustrate the point that contaminated forensic evidence of any kind (not just contaminated eyewitness evidence) can lead to a wrongful conviction. Because DNA evidence generally is regarded as the gold standard of forensic evidence, I decided to use that as my example. To find an illustrative case, I conducted a Google search using terms like “DNA contamination” and “wrongful conviction.” That’s how I stumbled upon the story of Gary Leiterman.The problem is, that because the prosecution viewed the DNA evidence as accurate, they had to explain how 4-year-old Ruelas's DNA made it onto Mixer's hand. Their explanation was that he was also present at the crime, and bleeding. Mind you, the crime took place around 3am. It seems highly unlikely that a 4-year-old would be there, nor is there any reason to believe Leiterman and Ruelas knew each other. And the plot thickens:
The story begins with a tragic event: 23-year-old University of Michigan law student Jane Mixer was shot in the head with a .22-caliber gun in the early morning hours of March 21, 1969, and her body was dumped in a graveyard. She had arranged to meet a stranger named David Johnson at the student union on the evening of March 20, 1969, and he was supposed to drive her home to Muskegon, Michigan (about a 3-hour drive). She never made it. She was initially thought to be a victim of the infamous “Co-Ed Killer” (later found to be John Norman Collins), who was murdering women in the area at the time, but no direct link to him was ever established.
Mixer’s murder remained unsolved until a cold-case analysis of DNA from the crime scene was conducted in a Michigan State Police forensic lab in 2002. That analysis uncovered two previously undetected DNA profiles that matched the profiles of two men who were included in a federal DNA database because they had recently committed crimes. One of those men was John Ruelas, who murdered his mother in early 2002. His DNA was found on a blood spot taken from Mixer’s hand in 1969. The other was Leiterman, who recently had forged a prescription for pain medication. His DNA was found on a piece of pantyhose that Mixer had been wearing that day. Because Ruelas was only 4 years old in 1969, he was ruled out as a suspect, so only Leiterman remained a suspect. In 2005, he was sentenced to life in prison without the possibility of parole.
The timing of the DNA analyses is striking. On October 24, 2001, the Mixer evidence from 1969 was pulled out of storage and taken to the Michigan State Police crime lab for processing. It was analyzed in March and April of 2002. Independently, evidence from the 2002 Ruelas murder case arrived at the lab on January 29, 2002, and was analyzed on February 20 and 21, 2002. At this point, it was unclear who had murdered Ruelas’s mother, so the evidence was sent to the lab to help with the investigation. On February 22, 2002, a mouth swab from Leiterman arrived in the lab for initial processing so that his DNA profile could be entered into the federal database.So these three people, who were previously considered unconnected, all had DNA evidence being analyzed at this lab at the same time. The DNA evidence obtained from Mixer's pantyhose, which the lab said belonged to Leiterman, was not blood or semen, but saliva, the exact kind of sample sent to the lab for processing. Further, Wixted continues discussing the Co-Ed Killer John Collins, who was active in that area, at that time, and many of his crimes matched the details of the Mixer case. It seems much more likely that Collins, not Leiterman, committed the murder. The problem is that, if you can't trust the DNA evidence, what can you trust? What additional evidence could possibly be found to overturn Leiterman's conviction?
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