SALEM, Mass. (AP) — A chemist who used to testify for prosecutors stood up in a sixth Massachusetts courthouse Monday and again pleaded her innocence in connection with a state drug lab scandal.

Annie Dookhan's plea in Essex Superior Court on a charge of misleading the grand jury, prosecutor and judge marked the end of her half-dozen arraignments following a 27-count indictment.

Authorities have accused her of wrongdoing that includes fabricating drug test results and tampering with evidence while testing samples. They also allege she lied about having a master's degree in chemistry while testifying as an expert witness during drug prosecutions.

The 35-year-old Franklin, Mass., woman remained free on her prior bail of $10,000. Dookhan and her attorney declined to comment outside the courtroom. She is due back in court Friday for a pre-trial conference in Middlesex County.

The scandal threatens to unravel thousands of drug convictions. Judges have let about 200 drug defendants out of custody and put their cases on hold while legal challenges go through the courts. Authorities said some have committed new crimes in the meantime.

State police closed the Boston lab in August after taking over the facility and learning about the depths of Dookhan's alleged misdeeds. She resigned months earlier during a state Department of Public Health internal investigation.

Authorities say Dookhan tested more than 60,000 samples involving 34,000 defendants during her nine years at the lab.

She allegedly told police she sometimes contaminated a sample with a known narcotic if it tested negative for drugs, and other times would label a sample positive without testing it.

Also Monday, a Massachusetts prison inmate filed a federal civil rights lawsuit against Dookhan, a Boston police official, the state and the offices of the Suffolk and Norfolk district attorneys. Continued...