Massachusetts crime lab chemist pleads not guilty in sixth arraignment By Daniel Lovering CAMBRIDGE, Massachusetts (Reuters) - A former Massachusetts crime lab chemist accused of falsifying evidence linked to as many as 34,000 cases pleaded not guilty on Monday to obstruction of justice in her sixth and final arraignment. In an appearance at Essex Superior Court in Salem, Annie Dookhan denied the charge, related to allegations that she falsely claimed to hold a master's degree, a court official said. Dookhan was charged in six districts in the Boston area in the evidence tampering case, which rocked the Massachusetts state crime lab. Investigators last year said they had identified some 10,000 people convicted or accused of crimes based on evidence handled by Dookhan, 35, who was arrested in September. As of last week, the state Department of Correction had released 286 people pending new trials as a result of Dookhan's activities at the Hinton State Laboratory Institute in Boston, where she worked for nine years. Prosecutors allege she tampered with drug evidence and faked test results at the lab, and that she had gotten the job by falsely claiming she had a master's degree in chemistry from the University of Massachusetts. Dookhan was accused of making the claim while testifying under oath as an expert witness in 14 separate criminal trials, according to court documents. Dookhan told officials she "screwed up big time," according to a police report. It said she told officials that no one else at the lab knew what she had done and that she was just trying to get more work done. She allegedly altered substances in vials to cover up her practice of "dry labbing," or visually identifying samples without doing the proper chemical testing. Dookhan was removed from the testing lab in June 2011 and resigned in March 2012. Investigators have begun a file-by-file review of more than 60,000 drug samples handled by Dookhan and tied to 34,000 cases. She was scheduled to appear in court in Middlesex County on Friday for a pre-trial conference. (This story corrects headline and first paragraph to say chemist pleaded not guilty in the last of six arraignments (not to a sixth charge of obstruction of justice). Paragraph 2 changed to reflect correction; paragraph three added for further clarification) Editing by Barbara Goldberg and Leslie Adler