(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.