Story highlights Annie Dookhan pleads guilty to tampering with evidence, perjury, obstruction of justice

300 drug convictions have been put on hold in one county alone

Dookhan cut corners in criminal cases, altered samples to cover up

Authorities: One person set free because of Dookhan went on to kill someone

A former Massachusetts crime lab chemist accused of mishandling evidence affecting hundreds, and perhaps thousands, of criminal cases was sentenced Friday to three to five years in prison after pleading guilty to 27 counts.

Annie Dookhan, 36, was arrested last year, accused of cutting corners by visually identifying alleged drug samples instead of performing chemical tests, and then altering the samples to cover up the practice.

More than 300 drug convictions involving Dookhan's tests -- conducted from 2003 to 2012 -- have been put on hold since last year in Suffolk County alone, Suffolk County District Attorney spokesman Jake Wark said.

Dookhan also was accused of falsely claiming, while testifying as an expert witness at a criminal trial, that she had a master's degree in chemistry from the University of Massachusetts. A defendant's conviction was overturned because of this, and authorities allege he killed someone in May, after his release.

"Annie Dookhan's egregious misconduct sent ripple effects throughout our entire criminal justice system," Attorney General Martha Coakley said in a statement. "Her deliberate decision to tamper with drug evidence and fabricate test results harmed the integrity of the system and put the public's safety at risk."

Dookhan pleaded guilty Friday to tampering with evidence, perjury, obstruction of justice and falsely claiming to holding a master's degree.

She said little during Friday's hearing in Boston, other than repeatedly saying, "Yes, your honor," to questions such as whether she understood the consequences of her guilty pleas.

The judge also ordered that she serve two years of probation after serving the prison time.

Governor: 40,000 defendants could be affected

In August, Gov. Deval Patrick's administration said the cases of more than 40,000 defendants could be affected by Dookhan's tampering. Reviews of all the cases she handled are under way.

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 at the William A. Hinton State Laboratory in Jamaica Plain 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 in September 2012.

Authorities: Released man accused in killing

Dookhan's false testimony about her credentials in a Plymouth County drug trial led to the release of a man who went on to be accused of murder, Plymouth County District Attorney Timothy Cruz said.

Donta Hood was convicted of a cocaine charge in 2009, in a trial in which Dookhan -- as an expert witness -- falsely testified that she had a master's degree, authorities said.

Hood was released in November 2012. Cruz said he wasn't able to retry Evans on the drug charge because the evidence in the case was destroyed. Storage space had been at a premium, he said, and no one thought it would be needed again.

After his release, Hood was arrested twice -- first, on a gun possession charge. While out on bail for the gun charge, he allegedly shot and killed Charles Evans in Brockton, Massachusetts, in May, authorities said.

"There's no bigger pain than somebody being released that goes out and kills somebody," Cruz told CNN.

Evans' family declined to comment.

Chemist in Massachusetts drug sample case lied about degree

Dookhan also declined CNN's request for comment about her case.

At a court proceeding earlier this year, Dookhan's lawyer, Nicholas Gordon, said that she took shortcuts in the lab to get more cases done to help her career, never considering the negative consequences it could have for criminal cases.

"The furthest thing from her mind is that this is going to ultimately cost millions of dollars, (And that) it's going to throw the entire Massachusetts criminal justice system into a tailspin," Gordon said in court.

An investigation revealed that not only did Dookhan not have a master's degree, but she never took master's-level classes, prosecutors said.

Some of the obstruction charges stem from instances in which authorities relied on tampered evidence in criminal proceedings, prosecutors said.