40,000 texts: Federal jury hears final case against ex-detective accused of killing pregnant woman

Closing arguments are scheduled for Friday in the federal trial of Matthew Farwell, a former Stoughton police detective accused of murdering Sandra Birchmore in 2021.

Farwell, now 40, faces charges in federal court in Boston after local authorities initially ruled Birchmore's death a suicide. Prosecutors contend the detective killed the 23-year-old teacher's aide to prevent her from revealing a sexual relationship that began when she was 15 and was pregnant with what he believed was his child. Farwell was married at the time and served in the same police department where Birchmore had participated in a youth program as a child.

The defense acknowledges Farwell had an extramarital relationship with Birchmore but maintains he did not kill her and did not engage in sexual activity until she was an adult. Farwell's lawyers argue he went to her apartment to end the relationship and that Birchmore, who faced financial strain and mental health challenges, took her own life. They point to her history of psychiatric medication starting at age 6 and previous suicide attempts as evidence of her vulnerability.

Federal investigators took over the case in 2023 after finding the local probe rushed. The FBI determined that local police interviewed Farwell for only 15 minutes in a parking lot without taking notes, examining him for injuries, or collecting DNA samples. They also reviewed his phone only after he had deleted texts with Birchmore. Billy Farwell, the defendant's twin brother, testified that the lead investigator, a family friend, told him he needed the case closed like he needed a bullet in the head. The Massachusetts State Police and medical examiner have since changed the official cause of death from suicide to undetermined.

Prosecutors presented digital forensics showing Birchmore's phone stopped moving at 9:40 p.m. on February 1, 2021. Lobby security footage recorded Farwell leaving her building three minutes later. A forensic expert hired by the prosecution, Dr. William Smock, testified that Birchmore was strangled with a duffel bag strap and struggled before dying. The defense countered with Dr. Thomas Andrew, a former chief medical examiner in New Hampshire, who stated the evidence pointed to hanging and dismissed the homicide determination.

The FBI recovered approximately 40,000 text messages between Farwell and Birchmore. These exchanges included reminiscences about sex when Birchmore was 15, an age that did not meet the consent threshold in Massachusetts. The texts also detailed contentious arguments as Birchmore pressed Farwell to impregnate her and threatened to inform his wife of their relationship. A paternity test later determined a different man was the father of the unborn child. Birchmore had booked a maternity shoot and was searching for a baby shower venue before her death. A stroller in its original box and an ultrasound photo were found in her apartment.

The trial is set to conclude with final statements from both legal teams on Friday. The jury will then deliberate on the charges against Farwell, whose defense team asserts the local investigation was compromised by personal connections among investigators.