NORTHAMPTON, Mass. (AP) — A chemist at a state crime lab tampered with drug evidence, authorities said Sunday in Massachusetts, where a chemist at another lab was accused last year of faking test results in a scandal that threw thousands of criminal cases into question.

Sonja Farak, who works at a lab in Amherst, in western Massachusetts, removed from a case file a substance that tested positive for cocaine and replaced it with one that didn't, state Attorney General Martha Coakley said. Evidence suggests Farak stole drugs that had already been tested, prosecutors said.

Farak, of Northampton, was arrested Saturday. She also is charged with possession of heroin and cocaine.

The lab contacted state police on Friday to report a discrepancy in inventory, Coakley said at a Boston news conference. Officials do not believe Farak's tampering will undermine evidence, she said.

"On its face, the allegations against this chemist do not implicate the reliability of testing done or fairness to defendants," she said.

Last month, the other chemist, Annie Dookhan, was indicted on 27 charges in a case that threatens to unravel thousands of drug convictions. Dookhan, of Franklin, resigned in March during an internal investigation by the state Department of Public Health. She has pleaded not guilty.

State police said they closed the Boston lab where she worked in August after taking over its operation and discovering the extent of her misconduct.

The accusations against Farak, unlike those against Dookhan, don't involve falsification of tests or dry labbing, visually identifying samples instead of performing required chemical testing, the attorney general said.

Farak does not have a listed phone number, and it was unclear whether she had a lawyer. Continued...