A chemist at the center of a scandal at a Massachusetts drug lab 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 he says he did not commit.

A lawyer for Shawn Drumgold asked a judge Wednesday 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.

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

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

Dookhan was in court, but pleaded the Fifth Amendment through her attorney. (AP)

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