Story highlights The convictions were tainted by a scandal in the drug lab

Annie Dookhan was convicted of falsifying results of drug tests

(CNN) Because of a lab chemist's widespread criminal misconduct in analyzing drug samples, about 95% of 20,000 drug convictions in Massachusetts have been dismissed, according to the American Civil Liberties Union of Massachusetts.

"That is a victory for regular people, for people who've been tarnished by these drug convictions," said Carl Williams, a staff attorney for the ACLU.

Those drug convictions had relied on analysis from Annie Dookhan, a former chemist for the Department of Public Health. Dookhan worked testing drug samples submitted by law enforcement agencies from 2003 until 2012, when investigators accused her of contaminating drug samples, falsifying results, and mishandling evidence.

Investigators said she admitted to intentionally contaminating some samples to turn them from negative samples into positive samples. She also admitted to "dry labbing" in which she tested a few samples but reported the same results for multiple other samples.

Dookhan pleaded guilty in November 2013 to 27 criminal counts in all, including charges of perjury, evidence tampering and obstruction of justice. She was sentenced to 3 to 5 years in prison, and was released last year

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