Evidence

Is DNA infallible proof? Contamination, stats can lead to injustice, prof says


DNA evidence may seem rock solid, but in some cases it has pointed to the wrong suspect.

Sometimes, contamination can provide a faulty conclusion, according to a New York Times op-ed by University of California at Hastings law professor Osagie Obasogie. He provides some examples.

DNA found on the fingernails of the victim of a November robbery and murder in San Jose, Calif., was put into a crime database, producing a hit. Authorities charged 26-year-old Lukis Anderson. But it turned out that Anderson was in the hospital on the night of the crime, where paramedics had taken him because of severe intoxication.

Anderson spent more than five months in jail before prosecutors recognized that he could not have been the perpetrator. Prosecutors now believe that Anderson’s DNA may have been transferred to the victim by the paramedics’ clothing or equipment. The theory is still under investigation, the op-ed says.

In another case, police in Germany searched for a serial killer linked to six murders through DNA, Obasogie says. In 2009, police recognized that the DNA was from cotton swabs used in the investigations, which had been contaminated with the DNA of the factory worker who made them.

Statistics can also be exaggerated, according to Obasogie. Frequently the claim is made that it is highly unlikely for two DNA profiles to match by coincidence. Yet a 2005 audit of about 65,000 profiles in Arizona’s DNA database found almost 150 pairs matched at a level considered sufficient to identify suspects. The profiles were clearly from different people, Obasogie says.

“For far too long,” Obasogie says, “we have allowed the myth of DNA infallibility to chip away at our skepticism of government’s prosecutorial power, undoubtedly leading to untold injustices. …

“The next Lukis Anderson could be you. Better hope your alibi is as well documented as his.”

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