By Daniel Lovering

CAMBRIDGE, Massachusetts (Reuters) - Massachusetts Governor Deval Patrick said on Thursday he expects criminal charges to be filed in the case of a chemist accused of mishandling drug evidence at a state crime lab, potentially affecting thousands of cases.

The chemist, Annie Dookhan, told investigators she "screwed up big time" by intentionally contaminating samples, forging approvals and failing to follow procedures, according to a police report.

Dookhan allegedly tampered with drug samples during her nine-year tenure at the state forensics lab in Jamaica Plain. She resigned in March, and a criminal investigation is under way. Dookhan has not been charged with a crime.

On Monday, officials began examining a first batch of about 1,100 cases of people who are already serving prison sentences based on potentially tainted evidence. On Thursday, a Massachusetts man was released from prison after being granted a new narcotics trial as a result of the crime lab investigation.

The governor said on Thursday that criminal charges should be brought in the misconduct case.

"I fully expect, and indeed I will say, I hope that there are charges," Patrick said. "I think that all of those who are accountable for the impact on individual cases need to be held accountable."

In an interview with detectives in August, Dookhan said she "would never falsify because it's someone's life on the line," but then admitted to intentionally contaminating samples "a few times" and "dry labbing" -- identifying samples without properly testing them -- for two to three years.

"I screwed up big time," she said, according to the report, which was posted on The Boston Globe's website this week. "I messed up. I messed up bad, it's my fault. I don't want the lab to get in trouble."

Dookhan, who was removed from the testing lab in June 2011, said no one else at the lab knew what she had done and that she had disobeyed orders even though she knew it was "wrong." Dookhan said she was simply trying to get more work done.

Asked why she had forged initials to signal approval of her work in a log book, she said, "There was no one available -- no one has the time -- I wanted to get the work done."

State police took over the lab in July and discovered Dookhan's mishandling of evidence was more widespread than previously thought. During her career at the lab, Dookhan handled more than 60,000 drug samples, potentially affecting 34,000 cases, the Department of Public Health said.

The governor ordered the lab closed in late August and last week established an office to oversee a review of criminal cases potentially affected by the "failures" there.

Department of Public Health Commissioner John Auerbach resigned in the wake of the scandal last week, saying "there was insufficient quality monitoring, reporting and investigating on the part of supervisors and managers" at the lab.

He denied responsibility for the actions of a "rogue chemist" and said, "The buck stops with me."

(Editing by Barbara Goldberg and Leslie Adler)