BOSTON (AP) — A call is being made for the appointment of an independent investigator to oversee the probe of the testing scandal at a state drug lab.

The Massachusetts Bar Association and the American Civil Liberties Union were among the groups to sign a letter sent on Wednesday to Attorney General Martha Coakley, asking her to appoint the outside investigator to fully examine what happened at the lab.

Former chemist Annie Dookhan has been accused of mishandling drug samples, potentially jeopardizing thousands of criminal cases.

Martin Healy, chief legal counsel for the bar association, said the crisis calls for a wider investigation to restore public confidence.

A spokesman for Coakley said the letter was under review, but added the office was surprised by the letter because it had been working with defense attorneys to conduct a “fair, complete and transparent” probe.