Closing arguments are expected Friday in the trial of a former Massachusetts police officer accused of killing a pregnant woman to keep her from revealing that they had been in a sexual relationship that began when she was 15.
Federal prosecutors say Matthew Farwell killed Sandra Birchmore, 23, and tried to stage her death as a suicide in 2021 after learning she was pregnant with what he thought was his child. At the time, Farwell was a married detective with the Stoughton Police Department, where Birchmore had participated in a youth program as a child.
Lawyers for Farwell, who is now 40, acknowledge he had an extramarital relationship with Birchmore. But they say he didn't kill her and didn't have sex with her until she was an adult.
The trial has unfolded in federal court in Boston, partly because local prosecutors never brought criminal charges.
Local police and investigators from the Massachusetts State Police, some with personal connections to Farwell, quickly concluded Birchmore's death was a suicide after she was found slumped on her apartment floor with a strap around her neck.
The state’s medical examiner, relying partly on information from police, also initially ruled that Birchmore died by suicide. The office has since changed the official cause of death to “undetermined.”
But Birchmore's friends and family never believed the teacher's aide had killed herself.
She had told dozens of friends about her pregnancy and, according to prosecutors, was thrilled to start her next chapter as a single mom. She had booked a maternity shoot, was searching for a venue for her baby shower and considering baby names. A stroller, still in the box, was found in her apartment along with an ultrasound photo pinned to her refrigerator.
The FBI began looking into Birchmore’s death in 2023, partly at the urging of a former deputy chief at the Stoughton Police Department who had led an internal affairs investigation into Farwell and several other officers accused of misconduct.
As they dug into the case, federal investigators concluded the local probe was rushed and compromised. Farwell was interviewed for just 15 minutes in a parking lot, they said. Investigators didn’t take notes, examine him for injuries or sample his DNA. Police did look at Farwell’s phone, but only after he had deleted texts with Birchmore.
Farwell’s twin brother, Billy Farwell, testified that the lead investigator — a longtime family friend — told him he wanted the case closed and needed the investigation like he needed a “bullet in the head.”
The FBI investigation uncovered about 40,000 texts between Farwell and Birchmore, including some in which they reminisced about having sex when she was 15 — too young to consent under Massachusetts law.
The text exchanges also showed how their relationship grew contentious as Birchmore pressed Farwell to get her pregnant — and threatened to tell his wife about their relationship if he didn’t. After she learned of her pregnancy in late 2020, texts showed they argued over what role, if any, Farwell would play in the child's life.
At the trial, a digital forensics expert testified that Birchmore’s phone stopped moving at 9:40 p.m. on Feb. 1, 2021 — three minutes before the lobby security camera recorded Farwell leaving her building on the night of her death.
An expert hired by prosecutors, Dr. William Smock, testified that Birchmore’s injuries indicated she was strangled with a duffel bag strap and that she struggled before dying.
The defense countered with their own expert, Dr. Thomas Andrew, the former chief medical examiner in New Hampshire, who said the evidence pointed to hanging. He dismissed Smock's determination that it was a homicide.
Farwell’s lawyers say he went to Birchmore’s apartment to break up with her, not kill her. They say Birchmore was broke and alone when she became pregnant, and took her own life.
A paternity test later revealed that a different man was the father of Birchmore's unborn child.
Farwell's legal team also leaned heavily on Birchmore's mental health challenges and attempted to show she was at risk of suicide. She began taking psychiatric medication at age 6, they said, attempted suicide as a teenager and wrote several times about suicide in her journals.
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