Former cop accused of killing pregnant woman and staging her death to look like a suicide

A former Massachusetts police officer is accused of killing a pregnant 23-year-old woman who he began sexually exploiting when she was a teenager and staging her death to look like a suicide, a federal indictment unsealed in Boston on Wednesday alleges.

Former Stoughton police officer Matthew Farwell allegedly strangled Sandra Birchmore to death in February 2021 after she told him she was pregnant with his child and "staged" her apartment "to make it appear as if Birchmore had committed suicide," the indictment stated.

He was indicted by a federal grand jury on one count of killing a witness or victim.

"We allege that Sandra Birchmore survived years of grooming, statutory rape and then sexual violence all at the hands of Matthew Farwell, who was employed throughout their relationship as an officer and then detective with the Stoughton Police Department. And when it became clear to Mr. Farwell that he could no longer control Ms. Birchmore, he silenced her permanently," acting U.S. Attorney Joshua Levy said during a press briefing on Wednesday.

Farwell, 38, was arrested Wednesday morning at a shopping center and is scheduled to appear in federal court in Boston on Wednesday afternoon, authorities said. ABC News has reached out to Farwell's attorney for comment.

Prosecutors alleged that Farwell befriended Birchmore after she joined a Stoughton Police Department youth program he was an instructor for and "essentially groomed her."

The indictment alleges that the two began a sexual relationship when Farwell was 27 and Birchmore was 15. Farwell allegedly engaged in sex acts with Birchmore when she was a minor while on duty as a police officer "falsely represented that he had worked certain hours" to conceal the activity, the DOJ said.

Their affair continued up until her death on Feb. 1, 2021, while Farwell was married with children, according to prosecutors. She was found dead in her Canton apartment on Feb. 4, 2021.

Prosecutors allege that after Birchmore told Farwell in October 2020 that she wanted a child of her own, the two "reached an agreement": He would try to impregnate her "in exchange for her silence about his criminal conduct (i.e., child sexual abuse) and years-long extramarital affair," a motion in support of pretrial detention stated.

Prosecutors allege that after Birchmore told Farwell in December 2020 that she was pregnant and wanted him to be more involved in the planning of the birth, he became angry and "was losing control."

"The information she possessed about his illegal conduct was in danger of slipping out," Levy said. "In fact, word started to get out about their relationship."

Less than two weeks before Birchmore was found dead, a friend called the Stoughton Police Department and disclosed the sexual relationship between Birchmore and Farwell, according to the DOJ. Farwell allegedly became "visibly angry" upon learning about that call and "started to lose his patience" and that she disclosed to friends that he had become physically violent with her, Levy said.

In one instance, Farwell allegedly held a pregnant Birchmore in a headlock and told her that he wished she were dead, prosecutors said.

"Then it all came to a head on Feb. 1, 2021," Levy said.

Prosecutors allege that Farwell went to Birchmore's apartment that evening wearing a mask "despite being well known as a resistant to COVID-19 mask mandates" and strangled her to death using a duffle bag strap, according to court filings. He then "used his knowledge and experience as a law enforcement officer" to stage her death to look like a suicide, Levy said.

He also allegedly lied repeatedly to Massachusetts State Police detectives investigating her death about the nature of their relationship, according to FBI Boston Special Agent in Charge Steve Kelleher. He allegedly told detectives that their sexual relationship began in 2020 -- when text messages with Birchmore showed it began in 2013, prosecutors claimed in court filings. He also allegedly told detectives they last had sex in October 2020, "attempting to avoid suspicion about whether he was the father of Birchmore’s unborn child," though "text messages indicate that Farwell met Birchmore to have sex after that date," court filings stated.

Before Birchmore's death, Farwell allegedly directed her to delete evidence of their sexual relationship, according to court filings.

"He attempted to cover his tracks to literally get away with murder, and he almost did, until today," Levy said.

State officials initially ruled Birchmore's death a suicide, though Levy said that over the past year, federal investigators uncovered "critical new information" and examined existing information, leading to the indictment. Levy did not elaborate on what initially led federal authorities to investigate Birchmore's death.

Kelleher said investigators reviewed tens of thousands of text messages, emails and financial records, as well as conducted dozens of interviews and analyzed the crime scene as part of their investigation.

He said the investigation "uncovered evidence inconsistent with someone dying by suicide" -- including the fact that Birchmore had reached out to a photographer to ask about booking a newborn photo shoot and to a friend about obtaining baby clothes in the hours leading up to her death.

She also was in the middle of doing laundry when she died, he said, calling the alleged murder "depraved."

"Committing murder to eliminate victims and witnesses is heinous and it shakes the very core of our justice system, which depends on people truthfully testifying to what they know," he said.

If convicted, Farwell faces a minimum sentence of life in prison. The charge is also eligible for the death penalty. Levy said the DOJ has not yet made a determination on seeking it.

Levy said they are sharing their information with local and state authorities so that they can assess whether any state charges may be warranted.

Farwell served as a police officer and then detective for the Stoughton Police Department from March 27, 2012, to April 1, 2022, according to the indictment.

Stoughton Police Chief Donna McNamara said the department supported the FBI in its investigation resulting in the indictment.

"The alleged murder of Sandra is a horrific injustice," McNamara said in a statement. "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."