Annie Dookhan's attorney filed a motion Friday claiming she never got a Miranda warning and her Fifth Amendment right against self-incrimination was violated.
The police statement she signed and a follow-up phone call happened under circumstances where a reasonable person "would not have felt free to end the interrogation," according to the motion.
Prosecutors plan to oppose the motion and look forward to making their case in court, a spokeswoman for Attorney General Martha Coakley said Monday.
In the statement she signed, Dookhan allegedly admitted making negative samples positive for narcotics, and "dry labbing," or testing some samples for drugs and assuming others were positive.
Authorities said Dookhan tested more than 60,000 drug samples involving 34,000 defendants at Hinton state lab, which they shut down last summer. She resigned months earlier during an internal probe. Hundreds of inmates have been released in the fallout from the scandal.
Authorities have previously said the only motive they can offer in the case is Dookhan's desire to be seen as a good worker. She has pleaded not guilty to charges including obstruction of justice and perjury after a 27-count indictment last year stemming from cases in six counties.
Court records show that one of the Massachusetts State Police officials who got the signed statement from Dookhan last August told grand jurors that she was cordial, alert and sober when they went to her Franklin home and she agreed to an interview.
"She was very cooperative," Detective Lt. Robert Irwin testified.
He also told grand jurors that he and Detective Capt. Joseph Mason showed Dookhan their badges and told her they were doing an investigation involving the lab and that she didn't have to speak to them if she didn't want to.
"She said, 'No, that's OK; I will talk to you,'" Irwin testified in October.
Irwin said that Dookhan's husband came home and asked if she was OK. She told him she was fine and kept talking to police.
Dookhan later left the room for several minutes after her husband asked to speak to her privately, according to the police official, who said Dookhan continued the interview once she returned.
The police official also testified that Dookhan told the investigators before they left that her husband privately had asked her if she should get a lawyer, but she told him no.
Dookhan, 35, of Franklin, is due back in Suffolk Superior Court in October, when her attorney and the prosecution are expected to make arguments about the defense's motion to suppress her statements to police.
Last week, a Suffolk Superior Court judge scheduled a Jan. 6 trial date for Dookhan.
Authorities have set up special court sessions to manage fallout from the lab scandal, whose effects have been felt through Massachusetts' criminal justice system.
At least 337 state prison inmates have been released as a result of the case, a state spokesman said last week.
The Massachusetts District Attorneys Association said at least 1,115 cases have been dismissed or not prosecuted because of Dookhan's involvement or due to problems with producing documents in a timely manner because of the lab's closure.
The state's highest court has decided that Superior Court judges have the power to release drug convicts from Dookhan-related cases on bail before they're granted new trials, if special magistrates who are handling the tainted cases make recommendations to do so.
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