District attorneys in Massachusetts are facing a key deadline as they continue to deal with the damage caused by the misconduct of a former state drug lab chemist.

The state’s highest court ordered the DAs to produce lists by Tuesday indicating how many of the approximately 24,000 tainted cases they would not or could not prosecute if new trials were ordered. Those cases would be dismissed.

Annie Dookhan pleaded guilty to tampering with evidence and falsifying thousands of tests in criminal drug cases, calling into question evidence used to prosecute the defendants.

The American Civil Liberties Union of Massachusetts estimates some 20,000 cases will be thrown out, which the group says could make it the largest mass dismissal of criminal convictions in U.S. history.

Dookhan served three years in prison.