Josiah Sutton and his friend Gregory Adams, 16 and 19 at the time, were accused for kidnapping and raping a 41 year old Houston woman although they both had alibis and didn’t match the profile from the victim’s original account. Sutton and Adams had agreed to provide police with blood samples while in custody, being sure that a DNA test would vindicate them. Their DNA was compared with a complex mixture of genetic material extracted from a vaginal swab. The mixture contained genetic material from at least three contributors, including the victim herself. The lab results however implicated Sutton and helped to convict him. In 1999, Sutton was found guilty of aggravated kidnapping and sexual assault and sentenced to 25 years in prison. His mother did everything to free her son, but no one proved willing to help. Not even the Innocence Project in New York, since it is a rule that they wouldn’t take cases where a definitive DNA match had been established.
But how certain is a „definitive DNA match“? DNA evidence is often considered a silver bullet – an infallible technique rooted in unassailable science. But science is only as reliable as the manner in which it is used. Advancements in DNA testing facilitate ever more emphasis on ever less substantial evidence. Even a trace of DNA can become the foundation of a case. But new techniques, such as low-copy number DNA analysis that are based on so-called „touch DNA“, can also more easily lead to errors. The strongest DNA profile on an object doesn’t always correspond to the person who most recently touched it. It might even correspond to somebody who never touched it at all (Read more). If the evidence contains complex mixtures of genetic material, as in the case of Sutton, the analysis becomes even more difficult. It has to be determined how many contributors are involved, and which alleles belong to whom. This is not an objective sciences and leaves room for interpretation.
How subjective the reading of complex mixture can be is illustrated by the following study by Itiel Dror, a cognitive neuroscientists at University College of London, and Greg Hampikian, biology and criminal-justice professor at Boise State University: In 2002, a defendant was found guilty of rape because two forensic scientists had concluded that he could not be excluded as a contributor to the DNA mixture from the rape kit. In 2010, Drop and Hampikian gave the DNA evidence to 17 lab technicians for examination. To ensure unbiased results, the context about the case was withheld. The result: only one of the 17 lab technicians concurred that the defendant could not be excluded as a contributor. Thus, the need to consider exculpatory evidence is greater than ever. But the justice system now allows little room for caution. On the contrary: pressure for results increases the threat of bias. Some analysts are even incentivised to produce inculpatory forensic evidence. In North Carolina, for example, state and local law enforcement agencies operating crime labs are compensated $600 for DNA analysis that results in a conviction.
In the case of Josiah Sutton, there was exculpatory evidence, but the jury never heard it. That was until a news segment about the Houston Police Department Crime Laboratory, aired on KHOU11, the local CBS affiliate. KHOU11 obtained dozens of DNA profiles processed by the Houston Police Department Crime Laboratory and sent them to independent experts for analysis. And the results were shocking: Apparently Houston police technicians were routinely misinterpreting even the most basic samples. “If this is incompetence, it’s gross incompetence … and repeated gross incompetence,” William Thompson, an attorney and criminology professor at the University of California at Irvine and forensic-DNA skeptic said. Thompson and his wife, also an attorney ,looked at the DNA tests from Sutton’s case and found obvious errors. On the one hand, there were inconsistencies in the DNA profiles from the victim due to typing errors, and on the other hand, Sutton’s DNA didn’t match the rape kit. As a result the DNA evidence was reprocessed by a private testing facility which confirmed Thompson’s findings. Sutton was subsequently released from prison. But after spending more than four years in prison, Sutton who was a promising football player with a college career ahead of him, never recovered, his mother said.
The lab analyst who was responsible for this errors was fired from the Houston crime lab, but later reinstated after her lawyer argued that her errors were product of systemic failures. Sutton’s case became one of the central pillars of a public inquiry into practices at the lab. The lab ultimately had to be closed down (Read more). It later reopened as Houston Forensic Science Center, a new entity independent of the police department. „I think it’s important for the forensic side to have that independence, so we can narrow it down without worrying about which side is going to benefit or profit from it, just narrowing it down to what we think is the accurate information,” Daniel Garner, the center’s head, told a local reporter.
Source: The Atlantic