AMHERST, Mass. (WHDH) -- A state crime lab chemist is now at the center of another drug testing controversy. Sonja Farak, 35, was arrested and charged with tampering with drug evidence and two counts of possession of drugs.

“After testing drugs, determining them to be the actual drugs, cocaine and heroin, the allegation is that this chemist then removed that substance the real substance, substituted a counterfeit substance in order to cover the tracks of what she had done already,” said Attorney General Martha Coakley.

Police said the discovery was made by supervisors at the Amherst state crime lab where Farak works. The lab is currently handling 750 cases, but in light of the investigation it will temporarily close. For now, prosecutors say there's no reason to believe any results have been compromised.

“In other words, these drugs were tested, they were tested fairly. The certificates were not impeached in any way, but we allege for personal use that the drugs were then taken and in her possession,” said Coakley.

According to Attorney General Martha Coakley, details of the Farak case bear no resemblance to the scandal surrounding disgraced chemist Annie Dookhan.

“The behavior at least as we know the alleged motives are completely opposite in this case. They are completely different sets of behavior,” said Coakley.

Dookhan, who worked at the state's Jamaica Plain lab is accused of altering drug evidence and making up results. More than 200 defendants have been released from prison because of questions over evidence handled by that lab.

Police say stricter policies put in place after Dookhan's arrest helped lead to Farak's arrest.

“It was cooperation and alertness of coworkers in that laboratory in Amherst that brought this to our attention immediately,” said

Farak has worked for the state for the last 10 years. She's been a chemist at the lab in Amherst since 2004.