( CNN ) -- A second Massachusetts state chemist in just a few months has been accused of mishandling drug evidence , the attorney general 's office said Sunday . Sonja Farak , 35 , who worked at the Massachusetts State Crime Laboratory in Amherst , was arrested at her Northampton home Saturday night by Massachusetts State Police and is facing two counts of tampering with evidence , one count of possession of a Class A substance , and one count of possession of a Class B Substance , according to Attorney General Martha Coakley . Farak remained in jail Sunday , the attorney general 's office said . `` We allege that this chemist tampered with evidence , placing the integrity of that evidence in question , '' Coakley said in a statement . This arrest comes just three months after the arrest of Annie Dookhan , a former Massachusetts chemist at the William A. Hinton State Laboratory in Jamaica Plain , who is charged with obstruction of justice , mishandling of drug evidence and lying about holding a master 's degree in chemistry from the University of Massachusetts . Dookhan , 34 , faces charges in several counties in Massachusetts because she had previously testified in various trials in her former official capacity as a chemist . A preliminary investigation found that Dookhan may have touched 60,000 samples that were involved in 34,000 drug cases . Massachusetts authorities are reviewing the sentences of 1,140 people who are in prison after being convicted with evidence at least partly provided by Dookhan . It is still unknown whether the accusations against Farak will jeopardize other drug cases , and this most recent investigation is ongoing and is being treated separately from Dookhan 's . In a news conference Sunday regarding Farak 's arrest , Coakley noted that `` unlike our allegations against Annie Dookhan , this did not involve 'dry labbing ' or falsification of tests . On its face , the allegations against this chemist do not implicate the reliability of testing done or fairness to defendants . '' `` Dry labbing '' is the practice of merely visually identifying samples instead of performing the required chemical test , the attorney general said . The crime laboratory in Amherst stores and analyzes alleged controlled substances seized by local and state police . According to the news release from the attorney general 's office , workers at the Amherst laboratory contacted state police on Friday to report a discrepancy in the controlled substance inventory held in evidence . An investigation was immediately launched . Based on the investigation , authorities allege that Farak tampered with drug evidence at the lab . In one instance , it appeared that Farak had removed a substance from a case that had previously tested positive for cocaine and replaced it with a counterfeit substance that no longer tested positive , the release said . Authorities also determined that Farak allegedly possessed what appeared to be Class A and B substances , the release said . Brad Puffer , spokesman for the attorney general 's office , told CNN that the substances under investigation were heroin and cocaine . CNN 's attempts to reach an attorney representing Farak were unsuccessful . She is expected to be arraigned on Tuesday morning in Eastern Hampshire District Court . CNN 's Michael Martinez and Marlena Baldacci contributed to this report .
Massachusetts chemist accused of tampering with evidence , drug possession . Sonja Farak took heroin , cocaine from evidence inventory , attorney general alleges . Another chemist was accused of tampering , affecting 34,000 drug cases , in October .