BOSTON (AP) — Revelations that a chemist at the center of a scandal at a Massachusetts drug lab might have lied about her educational background have given defense attorneys new grounds to challenge her credibility.

Annie Dookhan, whose alleged mishandling of drug samples at the lab has thrown thousands of criminal cases into question, testified under oath that she holds a master's degree in chemistry from the University of Massachusetts and also listed that degree on her resume. But school officials say they have no record of her receiving an advanced degree or taking graduate courses there.

Defense attorneys say that raises even more doubts about her work at the lab.

"If, in fact, she falsified her education or qualifications, we are even more deeply concerned about what she might have done in terms of testing the drugs," said Anne Goldbach, forensics services director for the Committee for Public Counsel Services, the state's public defender agency.

State police say Dookhan tested more than 60,000 drug samples submitted in the cases of about 34,000 defendants during her nine years at the lab. She resigned in March amid an internal investigation by the Department of Public Health.

After state police took over the lab in July as part of a state budget directive, they said they discovered her alleged violations were much more extensive than previously believed and went beyond sloppiness into "malfeasance" and "deliberate mishandling" of drug samples.

Dookhan has not responded to repeated requests for comments from The Associated Press. No one answered the door at her home in Franklin on Tuesday. Her husband and father did not respond to requests for comment on her claim that she received a master's degree.

Asked about her educational background when she testified under oath during the 2010 trial of Larry Blue, a Boston man charged with cocaine trafficking and weapons offenses, Dookhan said she had a bachelor's degree in biochemistry and a master's degree in chemistry, both from the University of Massachusetts.

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DeWayne Lehman, a spokesman for UMass-Boston, confirmed that Dookhan received a bachelor of science in biochemistry from the school in 2001, but said there is no record of her receiving a master's degree in chemistry, as she listed on her resume and said in sworn testimony, according to a transcript.

"We have no record of her doing subsequent graduate work at our campus," Lehman said.

The registrar's office at UMass-Boston also said it had no record of her receiving a master's degree, as did officials at UMass campuses in Lowell, North Dartmouth and Amherst. The Worcester campus does not offer a master's degree program in chemistry.

A spokesman for the Executive Office of Health and Human Services, which had overseen the lab, said Dookhan deliberately misled officials about her qualifications. He said she was hired Nov. 3, 2003, for a Chemist I position after meeting the minimum entrance requirements and was reclassified a Chemist II two years later.

"While neither of the positions she held required a Master's Degree, it is now clear that she intentionally misled the Department about her education during the course of her employment," HHS communications director Alec Loftus said in a written statement.

Blue was convicted of trafficking between 14 and 28 grams of cocaine, a drug violation in a school zone, possession of marijuana and weapons charges. He was sentenced to 10 years and one day in prison.

Blue's trial lawyer, Arnold Abelow, said that if Dookhan lied about her education, it calls her testimony about the drugs into question.

"If she's fudging her qualifications as being an expert, then how can you trust her analysis of the drugs?" Abelow said.

State police have not said exactly what Dookhan allegedly did wrong at the lab.

But Max Stern, president of the Massachusetts Association of Criminal Defense Lawyers, said he was told in a meeting with Gov. Deval Patrick and other administration officials that Dookhan is accused of deliberately tampering with some drug samples, including the weight of the samples, which can affect the length of prison sentences given to people convicted of drug offenses.

Attorney General Martha Coakley is conducting a criminal investigation. Dookhan has not been charged.

Investigators have not described Dookhan's possible motive for mishandling drug samples.

It is also unclear why she would fabricate having a master's degree.

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Associated Press writer Rodrique Ngowi contributed to this report.