BOSTON (AP) — A former Massachusetts police officer pleaded not guilty Wednesday to charges of killing a woman he is accused of sexually exploiting when she was underage and then trying to stage the death as a suicide after she told him she was pregnant.

Matthew Farwell entered the plea during an initial appearance in federal court in Boston. He was handcuffed and led out of the room. A follow-up court hearing was scheduled for Oct. 17.

Farwell was arrested at a shopping plaza in the city of Revere on Wednesday after he was indicted on charges he strangled Sandra Birchmore in early 2021 after she told him she was pregnant and he was the father. Birchmore was 23 years old.

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

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.

FBI Assistant Special Agent in Charge Stephen Kelleher said Birchmore was excited when she found out she was pregnant and texted Farwell a poster she made celebrating the pregnancy.

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 used his police knowledge to stage her apartment to make it look as though she had died by suicide, according to the indictment.

On some occasions, Farwell had been on duty when he sexually abused Birchmore as a minor and he falsely claimed certain work hours to hide that offending behavior, court documents say.

Margo Lindauer, an expert in intimate partner violence who teaches at Vermont Law School, told GBH News that the power differential between Farwell and Birchmore was a huge risk factor for lethal violence.

“She was his student. He was a police officer. She was a civilian. She was groomed,” Lindauer said. “She had a history of mental health and family problems that were exploited. And there was just this horrible cacophony of risk factors that she was victim to.”

There were 19 domestic violence homicide victims last year in Massachusetts, according to Jane Doe Inc., The Massachusetts Coalition Against Sexual Assault and Domestic Violence.

If Farwell is convicted, the killing of Birchmore would bring the domestic violence homicide tally for 2021 to 16.

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 minimum sentence of life in prison. Acting U.S. Attorney Joshua Levy on Wednesday declined to comment on whether federal authorities would seek to impose the death penalty if Farwell is found guilty.

Perry reported from Meredith, New Hampshire.

GBH News reporter Chris Burrell contributed reporting.