Forensic evidence - DNA on a victim, gunshot residue on a hand, fingerprints on a weapon - holds a special place in courtrooms, often treated as irrefutable proof that police have nabbed the bad guy. But the labs processing that prized evidence can sometimes become the suspects.
Last month, the Baltimore Police Department disclosed that its lab employees were leaving their own DNA on crime scene evidence. Lab director Edgar Koch lost his job because of the contamination, which had gone unidentified for years because the lab didn't take the basic step of cataloging employee DNA in a database.
The city's top prosecutor and police commissioner say the crime lab produces quality work that stands up in court.
"The vast majority of our lab employees are incredibly smart and talented people, scientists by trade," Police Commissioner Frederick H. Bealefeld III said, pointing to an employee who developed a date rape drug test used nationally. "They have done a lot to advance our lab."
But in recent years, defense attorneys have uncovered problems with the way crime labs across Maryland handle forensic evidence, and they've questioned the credentials of some prominent analysts. Last year, a Maryland State Police ballistics expert killed himself when it became known that he'd lied about his schooling. And years before the DNA scandal, the Baltimore lab admitted that its gunshot residue evidence could be tainted, in part because police firing ranges were too close to the lab area.
Even before the recent revelations about DNA processing in Baltimore, state legislators were so concerned about crime lab standards that they gave the Department of Health and Mental Hygiene oversight, beginning in 2011.
"Labs make mistakes. Scientists make mistakes. Published research can be wrong," said Walter Rowe, chairman of the nation's oldest forensic science department, at George Washington University.
"Most people's attitude toward science is that they're apt to accept its findings as gospel. There are some areas where the science is rock solid and incontrovertible. But there are other areas where we just think we know what's going on."
Each time a problem comes to light, defense attorneys warn that hundreds of cases could be jeopardized. But sweeping reviews, such as one undertaken in Houston five years ago when an audit revealed possible DNA contamination, often prove too costly and laborious, local defense attorneys say.
