A former Massachusetts police officer is accused of murdering a pregnant woman he had groomed as a teenager, and staging the scene to make it appear as a suicide.

A former Massachusetts police officer was arrested on charges of grooming a teenage girl, having sex with her when she was an adult, and killing her in her apartment after she revealed she was pregnant with his child, making it appear as a suicide.

Matthew Farwell, 38, was indicted on charges of killing Sandra Birchmore, 23, to conceal his sexual offenses. He was arrested at a shopping plaza in Revere on Wednesday.

For 10 years, from 2012 to 2022, Farwell served as an officer with the police department in Stoughton, which is located south of Boston. The reason for his departure from the department was not immediately apparent.

According to the indictment in U.S. District Court in Massachusetts, Birchmore started participating in the police explorers program at the age of 12. Court documents allege that Farwell, a police explorers volunteer, used his authority and access to groom, sexually exploit, and then sexually abuse Birchmore when she was 15. The abuse continued even after she became an adult.

The indictment alleges that during certain shifts, while Farwell was supposed to be carrying out his duties as a Stoughton police officer, he was instead involved in sexual activities with Birchmore.

According to an affidavit by FBI Special Agent Chenee Castruita, Farwell committed this murder in part to prevent Birchmore from disclosing to authorities information about Farwell's commission or possible commission of one or more crimes, including coercion and enticement, deprivation of rights under color of law, and a then-ongoing wire fraud scheme.

"Birchmore's murder by Farwell was the result of years of abuse inflicted by Farwell."

According to the indictment, Farwell learned that Birchmore was pregnant in late 2020.

According to Kelleher, Birchmore was thrilled upon learning she was pregnant and subsequently texted Farwell a poster she created to commemorate the occasion. Additionally, she contacted a friend regarding baby clothes and a photographer about potential baby photos.

"Kelleher stated that Matthew Farwell's possession of a gun and badge did not grant him the right to violate the Constitution, and it did not entitle him to sexually exploit, abuse, and rape a child before killing her and her unborn baby in an attempt to conceal his alleged crimes. Kelleher described the allegations against Farwell as "depraved.""

Kelleher stated that investigators suspect Farwell faked her death in the apartment.

In the following month, a friend of Birchmore's contacted the Stoughton Police Department to report that Farwell had been having sexual relations with Birchmore. According to the indictment, Farwell is accused of strangling Birchmore on or around February 1, 2021, and subsequently using his police knowledge to stage her apartment to make it appear as though she had committed suicide.

Court documents allege that Farwell abused Birchmore as a minor while on duty and falsified work hours to conceal his offending behavior.

Castruita wrote that Farwell continued to sexually abuse Birchmore even after she became an adult, and he continued to have an extramarital sexual relationship with her until he killed her on February 1, 2021.

The FBI collaborated with the Stoughton Police Department in an investigation, as stated by Police Chief Donna McNamara on Wednesday.

"After Sandra Birchmore's death in her Canton apartment, I ordered a thorough and forceful internal affairs investigation, ensuring that every possible lead was pursued. The investigation's objective was to uncover the truth behind Sandra's murder, and no stone was left unturned. The allegations against the suspect, a former Stoughton Police Officer, represent the worst act of professional misconduct and human indecency I have witnessed in my nearly three-decade career in law enforcement."

In federal court in Boston on Wednesday, Farwell pleaded not guilty and was handcuffed and led out of the room. A detention hearing is scheduled for Sept. 10, and another hearing is scheduled for Oct. 17.

If convicted of killing a witness or victim, Farwell would face a minimum sentence of life in prison. The Associated Press reported that Acting U.S. Attorney Joshua Levy declined to comment on whether federal authorities would seek the death penalty if Farwell is found guilty, stating that the decision would be made by the Department of Justice.

Massachusetts has outlawed capital punishment.

The Associated Press contributed to this report.