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.

A former chemist at the lab, Annie Dookhan, has been accused of mishandling drug samples she tested, potentially jeopardizing thousands of criminal cases in Massachusetts.  

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

He said the independent investigator would have subpoena power but would not act as a prosecutor.

Coakley's office did not immediately respond to the letter. (AP)