PLW:Errors in DNA Testing Occur Regularly

Matthew T. Mangino
The Pennsylvania Law Weekly
September 8, 2015
Kareem Johnson was on Pennsylvania's death row as the result of a 2007 Philadelphia murder conviction. When Johnson allegedly killed Walter Smith, prosecutors suggested that he shot him at such close range that Smith's blood splashed onto Johnson's red Air Jordan baseball cap, according to The Philadelphia Inquirer.
In fact, assistant district attorney Michael Barry told jurors, "That hat that was left at the scene in the middle of the street has Kareem Johnson's sweat on it and has Walter Smith's blood on it. ... DNA is a witness. It is a silent, unflappable witness."
According to the Inquirer, prosecutors now concede that they misinterpreted the DNA. The blood was found on a black baseball cap that belonged to Smith—not on Johnson's red hat.
Organizations like The Innocence Project have touted the nearly infallible application of DNA in cases that have exonerated the innocent. The Innocence Project's website lists 330 DNA exonerations over the past 14 years. The website tells the stories of people like Joseph Abbitt, who spent 14 years in a North Carolina prison before DNA exonerated him; and Anthony Capozzi, who spent 20 years in prison in New York; and Paula Gray, who spent 24 years in an Illinois prison.
There are also cases in which DNA was successfully attacked at trial. The O.J. Simpson trial brought DNA collection and analysis into America's living rooms.
Attorney Barry Scheck, who later co-founded The Innocence Project, was one of Simpson's attorneys focusing on the DNA evidence. He told the Los Angeles Times on the 20th anniversary of the trial, "It was a watershed case, but not in ways that people suspect. We did not challenge the underlying reliability of DNA testing methods; we attacked the way that evidence was gathered and processed. We had a 21st century technology and 19th century evidence-collection methods."
In Italy, American student Amanda Knox, along with her boyfriend, was convicted—based in part on incriminating DNA evidence—of killing her roommate, Meredith Kercher. Her body was found in a student house that she shared with Knox. She had been repeatedly stabbed and slashed.
After the first trial, Knox was sentenced to 26 years in prison and her boyfriend to 25. In 2011, their convictions were overturned.
Knox then returned to the United States, but an Italian appellate court overturned the acquittal and upheld the guilty verdicts. Knox was then sentenced in absentia to 28 years in prison.
DNA collection and analysis played a prominent role in Knox's conviction and appeal. That collection and analysis had come under scrutiny.
"There are some worrying features in this particular case, maybe because the individuals live in the apartment and their DNA will be everywhere. That's the issue in this case. There's no dispute that they were in the apartment, but for legitimate reasons," professor Peter Gill, a lecturer of forensic genetics at Oslo University in Norway, told the Daily Mail. "The evidence is weak. What I'm saying is there are possibilities of transfers, of contamination, which has to be seriously considered."
On March 27, seven-and-a-half years after their arrest, Italy's highest court exonerated Knox and her boyfriend.
There are, and have always been, problems with DNA analysis. There are occasions when a crime scene has an enormous amount of evidence to analyze for DNA markers. For instance, when an offender commits a burglary by breaking through a window and in the process cuts himself and subsequently bleeds throughout the structure.
Even small samples are reliable—a strand of hair, a mouth swab or a semen sample. They are the sorts of high-template-number DNA samples that have been effectively used in successful prosecutions and exonerations. In these cases, there's plenty of material to test, normally only one person's DNA and for the most part the testing procedures are standard. As a result, reliable, definitive results are expected and provided.
More often than not there is very little DNA at a crime scene, if any at all.
Trace DNA samples are defined as any sample that falls below recommended thresholds at any stage of the analysis, from sample detection all the way through profile identifications. According to McClatchy DC, trace DNA is saddled with complications, creating confusion in and out of courtrooms and prompting a new realization that "forensic science can't always lead to clear-cut results."
Also of concern is the use of touch DNA—a very insignificant amount of residue DNA that's left on an object. The sample can be as small as a few human cells, according to McClatchy. This DNA can be replicated and tested, but a conclusive match can be difficult, if not impossible.
Working with small or contaminated samples can result in false positives or just erroneous analysis, resulting in incorrect outcomes.
"DNA tests are not now and have never been infallible. Errors in DNA testing occur regularly. DNA evidence has caused false incriminations and false convictions, and will continue to do so," William C. Thompson wrote for the Council of Responsible Genetics.
Thompson wrote, "When DNA evidence was first introduced, a number of experts testified that false positives are impossible in forensic DNA testing. Whether such claims are sinister or not, they are misleading, because humans are necessarily involved in conducting DNA tests."
At least two of the first 200 people exonerated by post-conviction DNA testing were convicted, in part, due to DNA testing errors. Thompson concluded in both cases a combination of technical problems in the laboratory and careless or mistaken interpretation of the test results produced inaccurate DNA matches.
Prosecutors, defense attorneys and the courts are trying to get a handle on how to properly present, defend and admit certain types of DNA evidence.
"This is something we are trying to figure out ourselves," Paul Cates, communications director for The Innocence Project, told McClatchy. "We realize that there's a lot of discussion about [low-template-number DNA] in the scientific community and we are doing our own research to figure out where we are on this."
The zeal to prosecute, or defend, has led to the use of DNA evidence that may not be as reliable as originally thought and is certainly not infallible, as some may have suggested in the past. 
Matthew T. Mangino is of counsel with Luxenberg, Garbett, Kelly & George. His book, "The Executioner's Toll, 2010," was released by McFarland & Co. Contact him at www.mattmangino.com and follow him on Twitter @MatthewTMangino.

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