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
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.
Plaintiff Jeffrey Solomon, also known as Jeffrey Banks, is currently serving a prison sentence in Middlesex County on unrelated charges. Last year, prosecutors decided not to pursue drug charges, including dealing cocaine, against Solomon after testing showed a substance certified as cocaine by Dookhan was not a narcotic.
In his suit, Solomon said he's a victim of perjury, threats and false evidence, and claims unspecified monetary damages.
The suit accuses the Boston police detective who arrested Solomon of destroying evidence and falsely testifying he found cocaine on Solomon.
The lawsuit alleges state health officials didn't respond properly after finding problems with Dookhan's work and claims Dookhan favored prosecutors because district attorneys and health officials failed to prohibit contact between chemists and prosecutors.
A spokesman for the Suffolk district attorney said the office hadn't seen the suit and couldn't comment.
A spokesman for the Norfolk district attorney referred questions to the attorney general's office, which defends his offices against suits. An email requesting comment was left with spokesman for the attorney general, as well as a health department spokeswoman. A Boston police spokeswoman said the department doesn't comment on pending litigation.