D.C. prosecutors criticize city crime labs handling of some DNA evidence

D.C. prosecutors have stopped sending DNA evidence to the citys new state-of-the-art crime lab after they said they discovered errors in the way analysts determined whether a sample can be linked to a suspect or a victim.

Prosecutors have hired two outside DNA experts to review 116 cases, including rapes and homicides, and have been notifying defense attorneys.

In one federal case, prosecutors said, the D.C. lab concluded that a defendants DNA could have been on the magazine of a gun seized as evidence. But an expert who reviewed the data said the lab should have interpreted the results to mean that the defendant was not the source of the DNA.

In other cases, prosecutors said, the lab either understated or overestimated the likelihood that a particular persons DNA was left at a crime scene.

Officials at the Department of Forensic Sciences, which is located in a $220million facility that opened in 2012, defend their work and say disagreements among scientists in the field are not uncommon. The dispute has essentially created a standoff between the city-run lab and federal prosecutors in the nations capital.

U.S. Attorney Ronald C. Machen Jr. said that his office has been paying to send evidence for testing at outside labs, and that so far an additional 102 cases have been farmed out. At the same time, independent experts are taking a fresh look at the cases analyzed by the Districts lab.

To date, we have not found any evidence to suggest any wrongful conviction and have not acted to dismiss any cases, Machen said in a statement. However, in an abundance of caution, we are conducting a rigorous review of the analysis done in current and older cases to ensure that criminal defendants are treated fairly.

Max M. Houck, the director of the Department of Forensic Sciences, said that the lab follows the same protocols in place at many city and state labs across the country, and that experts may disagree on how to interpret evidence. The lab has made recent improvements, he said, but he stands by the work done before those changes.

This is an estimate an estimate of probability, said Houck, a former FBI supervisor who worked in the agencys anthropology and trace evidence unit.

The issue is that their experts would do the analysis differently. Differently isnt wrong, Houck said. Its like a financial planner doing a financial assessment of someones net worth in U.S. currency and in Japanese yen. Theyre both correct, just different measurements.

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D.C. prosecutors criticize city crime labs handling of some DNA evidence