More than 20,000 criminal drug cases tied to disgraced state chemist Annie Dookhan are now set to be thrown out in what will be the largest mass dismissal of criminal convictions in U.S. history. Dookhan pleaded guilty to 27 counts of misleading investigators, filing false reports and tampering with evidence in 2013. She falsified evidence tied to thousands of drug cases over the course of several years. Reporter Shawn Musgraves has been covering the fallout of the Dookhan for the Boston Globe. He spoke with WGBH News' All Things Considered host Barbara Howard about the dismissal of the cases.