BOSTON (WHDH) -- Annie Dookhan has been the target of an investigation for years, but police arrested her Friday for fear she might take off after allegedly making a $4,000 withdrawal.

The 34-year-old chemist at the heart of the lab scandal is charged with obstructing justice and sources tell 7News that Dookhan has stopped cooperating with investigators. She was arraigned in a courtroom Friday filled with family members.

“What she would do is she would take narcotics, maybe 15 or 20 or 25 samples at a time. And she would group them in areas that she believed-  here are 25 cocaine samples and instead of testing all 25, she would test five of them and then she would call all 25 of them cocaine,” said prosecutor, John Verner.

The prosecution also revealed that Dookhan’s tests would come back positive even though the same batch tested by Boston and state police would have negative results.

“She would take known cocaine from an area that she knew was cocaine and actually add them to a sample to make it cocaine,” said Verner.

Dookhan worked at the state drug lab in Jamaica Plain since 2003. Two years ago she came under investigation based on one of her co-worker’s observations.

The lab shut down in August when the severity of Dookhan’s alleged evidence tampering came to light. The judicial system was thrown into chaos and possibly tens of thousands of convictions were compromised.

Dookhan was fitted with an ankle bracelet while in her cell. Her family posted the $10,000 cash bail and she was released late Friday after signing probation papers. She fought through a crowd of reporters to beat her 6 p.m. to 6 a.m. curfew.

She is a naturalized citizen, but was told she had to turn in her passport to authorities. She is due back in court on Dec. 3.