A chemist at the center of a Massachusetts drug lab scandal has exercised her Fifth Amendment right and has refused to testify in a drug case against a Boston man who once spent 15 years in prison for the slaying of a 12-year-old girl — a crime he says he did not commit.

A lawyer for Shawn Drumgold asked a judge on Oct. 10 to dismiss two drug charges because chemist Annie Dookhan's initials appear on a drug analysis form indicating she tested the suspected cocaine and heroin.

Prosecutors say Dookhan's name appears on a certificate only as a notary and not as a tester of the substances.

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

Material from The Associated Press was used in this report.