Koch had run the crime lab for the past decade. Defense attorneys and forensic experts after his firing Tuesday raised questions about the state's biggest and busiest crime lab, The Baltimore Sun reported Thursday.

Police spokesman Sterling Clifford said Koch was fired because of employees contaminating evidence with their own DNA and other "operational issues."

The DNA contamination did not lead to anyone being falsely accused of a crime, city officials said, but Baltimore State's Attorney Patricia Jessamy said she has asked her staff to review the potential effects of the DNA contamination on open and closed cases.

"There are some concerns," Mayor Sheila Dixon said. "We don't have the details yet to know if these cases are in jeopardy, so I can't speak on that publicly yet."

The contamination was revealed after a new DNA supervisor began entering employee DNA samples into a database and comparing them against "unknown" genetic profiles found in evidence from crime scenes.

About a dozen instances out of 2,500 unknown genetic profile turned out to be that of a lab employee, Clifford said.