BOSTON (AP) — A former Massachusetts police officer has been accused of killing a woman he first sexually exploited when she was underage and then trying to stage the death as a suicide.

Matthew Farwell was indicted Tuesday on charges he strangled Sandra Birchmore in early 2021 after she told him that she was pregnant and that he was the father. Birchmore was 23 years old at the time.

Farwell killed Birchmore to prevent authorities from finding out details of his sexual offense, according to allegations in the indictment.

He was due to make his first court appearance Wednesday afternoon. Phone messages seeking comment and left at listings for Farwell were not immediately returned, and it wasn’t clear who was representing him in court and could speak on his behalf.

Farwell worked as an officer for the police department in Stoughton, south of Boston, for 10 years, from 2012 until 2022. It wasn’t immediately clear why he left the department.

Birchmore began participating in the police explorers program when she was 12 years old, according to the indictment in U.S. District Court in Massachusetts.

Court documents say that Farwell, who was a police explorers volunteer, used his authority and access to groom, sexually exploit and then sexually abuse Birchmore when she was 15 and that he continued to have sex with her when she became an adult.

In late 2020, Birchmore found out she was pregnant and told Farwell, according to the indictment.

The next month, a friend of Birchmore’s called the Stoughton Police Department to tell them Farwell had been having sex with Birchmore. Farwell strangled Birchmore on about Feb. 1, 2021, and then staged her apartment to make it look like she had died by suicide, according to the indictment.

On some occasions, Farwell falsely claimed he had worked certain hours to hide that he had been sexually abusing Birchmore when she was a minor while he was on duty, court documents say.

Stoughton Police Chief Donna McNamara said Wednesday that the department had worked with other agencies, including the FBI, to investigate.

“The day after Sandra Birchmore was found dead in her Canton apartment, I ordered a lengthy and aggressive internal affairs investigation, the instructions of which made it clear that no stone should be left unturned,” McNamara said in a statement.

“The alleged murder of Sandra is a horrific injustice,” McNamara said. “The allegations against the suspect, a former Stoughton Police Officer, represent the single worst act of not just professional misconduct but indeed human indecency that I have observed in a nearly three-decade career in law enforcement.”

If convicted of killing a witness or victim, Farwell would face a sentence of death or life in prison.