Five former coworkers of a chemist at the center of a Massachusetts drug lab scandal are expected to offer the first public look at how drug samples were tested at the now-closed lab.

The chemists are expected to testify Oct. 11 during the drug trial of Shawn Drumgold, a Boston man who spent 15 years in prison after being wrongfully convicted of killing a 12-year-old girl in 1988.

Drumgold is charged with possession with intent to distribute cocaine and heroin. He denies the charges, and his lawyer claims chemist Annie Dookhan participated in testing the drugs.

Dookhan is charged with obstruction of justice for allegedly skirting protocols and faking test results at the lab.

Dookhan invoked her Fifth Amendment right and didn't testify on Oct. 10 during Drumgold's trial at Roxbury District Court.