(CNN) -- A former Massachusetts chemist has indicated she will plead guilty to charges stemming from an investigation into how she allegedly mishandled sensitive evidence affecting thousands of state criminal cases dating to 2003, according to a source with knowledge of the agreement.
In an open door lobby conference last week, Annie Dookhan asked prosecutors and the judge overseeing her case what the ramifications would be if she were to change her plea from not guilty to guilty, according to the source.
Prosecutors indicated they would seek a minimum of a five- to seven-year sentence if Dookhan were to plead guilty. Her lawyer, Nicholas Gordon, asked for a one-year maximum sentence, according to the source.
"After consideration of the submissions of the parties and the arguments of counsel before this judge on October 18, 2013, I have decided that, if the defendant were to plead guilty before me, I would not exceed a sentence of three to five years in state prison, with a probationary term to follow," Suffolk Superior Court Justice Carol Ball said, according to court documents.
Dookhan, 34, is facing 27 counts, including obstruction of justice, mishandling of drug evidence and lying about holding a master's degree in chemistry from the University of Massachusetts.
The list of defendants whose cases could be affected by the alleged drug tampering by the former Massachusetts chemist has grown to more than 40,000, according to Massachusetts Gov. Deval Patrick's administration.
Dookhan worked as a state chemist testing drug evidence submitted by law enforcement agencies from 2003 until March 2012, when she resigned, according to the Massachusetts attorney general's office.
The attorney general's office began a criminal investigation in July 2012, after Massachusetts State Police were tipped off by Dookhan's co-workers, who alleged her work might be unreliable. The investigation revealed that Dookhan allegedly had tampered with evidence by altering substances in vials that were being tested at the state lab, allegedly to cover up the practice of routinely "dry labbing" samples. "Dry labbing" is a term used for visually identifying samples instead of performing the required chemical test.
Authorities arrested Dookhan at her home in Franklin, Massachusetts, in September 2012.
Dookhan has pleaded not guilty to all charges.
In a statement from the Massachusetts attorney general's office, spokesman Brad Puffer said: "It is the defendant's decision whether or not to plead guilty and the judge's decision to determine the sentence. Our office has not agreed to any plea deal and we are prepared to go to trial and prove our case before a jury. The defendant has indicated to the court that she will likely change her plea to guilty."
A hearing in Dookhan's case that was scheduled for Wednesday has been canceled.
A new change of plea hearing has been scheduled for November 22, when Dookhan is expected to plead guilty.
Dookhan's attorney, Nicholas Gordon, could not be reached for comment Monday.
CNN's Morgan Winsor contributed to this report.