Crime

The 23-year-old teacher’s aide’s death was initially ruled a suicide before a forensic investigation years later determined that she was murdered.

By Darin Zullo

September 21, 2025 | 10:00 AM

5 minutes to read

Friday’s episode of NBC’s “Dateline” shed light on the case of Sandra Birchmore, a pregnant 23-year-old teacher’s aide who was allegedly killed by a Stoughton police officer who had groomed her since childhood.

“The Betrayal of Sandra Birchmore” featured interviews with Birchmore’s family members, her former boss, and Stoughton Police Chief Donna McNamara. Through her loved ones’ eyes, viewers had a chance to see the revelations that led a closed-case suicide to be blown open and ruled a homicide years after her 2021 death.

Former Stoughton police officer Matthew Farwell is the main suspect in Birchmore’s murder, according to officials. In August 2024, he was arrested and indicted by federal authorities on one count of killing a witness or victim, to which he pleaded not guilty.

In addition to giving the case national attention, the “Dateline” feature included insights into details that changed the course of the investigation. What initially seemed like an unexplainable murder unraveled into a harrowing story of grooming and abuse of power dynamics.

Here are five key moments from “The Betrayal of Sandra Birchmore” not to be missed:

Farwell claimed he wasn’t the father, only had a brief affair with Birchmore

The federal investigation into Birchmore’s death revealed evidence that suggests Birchmore and Farwell had had a sexual relationship since 2013, beginning when she was 15 and he was 27, according to officials. The two met when Birchmore was enrolled in the Stoughton Police Department’s Explorers Program.

However, Farwell has adamantly denied that he groomed Birchmore and says their affair didn’t start until 2020, when Birchmore was 22. When Birchmore revealed to him in October 2020 that she was pregnant, he insisted that he wasn’t the father, claiming that the timeline didn’t match up, according to officials.

Farwell also alleged that he visited Birchmore shortly before her death to break off their relationship, but her cousins didn’t buy it, insisting that she would have told someone, according to the show. Her cousins characterized her as an oversharer and said she wouldn’t have grieved over the relationship in silence, making them all the more suspicious that her death wasn’t a suicide.

Two more officers, including Farwell’s twin brother, had sexual relationships with Birchmore

Though Farwell is the main suspect at play, evidence showed he wasn’t the only Stoughton police officer who may have been sexually involved with Birchmore, according to officials. Text messages obtained by State Police indicated that Birchmore was also being pursued by Matthew’s twin brother, William Farwell, who texted her asking for sexual photos and videos of her.

Facebook messages found in the investigation linked Birchmore to a third Stoughton police officer, Robert Devine, who ran the Explorers Program, which she had been enrolled in since she was 12 years old. The messages between the two allegedly discussed meeting up for sex, according to officials.

All three officers had known Birchmore since she was a teenager, suggesting some harrowing possibilities of when they may have begun pursuing her. In an interview featured in Friday’s episode of “Dateline,” McNamara expressed her disgust at this abuse of the power dynamic between Birchmore and the three officers.

“It’s just horrific to find this information out about people that are supposed to be protecting others,” McNamara said in the interview. “They dehumanized her in their text messaging, in their interactions, and it’s vile.”

McNamara’s report revealed crucial details that Birchmore’s family hoped would finally lead to a murder investigation, but to no avail. State Police insisted there was no evidence that Farwell killed her, and it took growing media attention to reignite the search for the truth, according to the show.

Investigative journalist Michele McPhee found herself questioning the State Police investigation and kept chasing the story, a “Dateline” interview revealed. Kirk Minihane and Dave Cullinane, hosts of the true crime podcast “The Case,” weren’t convinced it was a suicide either, focusing on the Birchmore case for an entire season of their podcast.

The months of effort that Minihane and Cullinane spent pushing for access to evidence finally paid off when the district attorney’s office turned over footage from Birchmore’s apartment building. The footage showed Farwell entering and leaving her apartment on the night of her death.

After the footage was released, FBI agents at last got in touch with Birchmore’s family to continue investigating. If it hadn’t gone viral on TikTok and been spotlighted on “The Case,” the investigation might have prematurely reached its end, according to the show.

Drama surrounding Karen Read trial helped call attention to Birchmore case

What also helped keep the Birchmore case’s flame alive was another high-profile murder case happening in the same county: the Karen Read trial. The defense in that case alleged that State Police had botched their investigation, and a jury ultimately acquitted her of second-degree murder.

The body of Boston Police Officer John O’Keefe, who Read was alleged to have murdered, was found in Canton, the same town where Birchmore was found dead. The overlap in State Police action between the two cases only furthered suspicions, according to the show.

Sure enough, after Birchmore’s aunt filed a wrongful death lawsuit and hired forensic pathologist Dr. Michael Baden to review her autopsy report, his findings determined that her death was a homicide. Baden’s investigation revealed that Birchmore had been strangled, completely altering the course of the case even before the FBI came forward with their findings, according to the show.

Evidence revealed Farwell was not the father of Birchmore’s child

Forensic evidence from the FBI revealed that someone had used force against Birchmore and a struggle ensued. The affidavit cited a broken necklace found at the scene of the crime, which was never mentioned in the police reports.

A closer examination of the timeline surrounding Birchmore’s death also revealed a chilling coincidence. Less than 13 hours after Farwell allegedly murdered Birchmore and her unborn baby, his own third child with his wife was born, according to the affidavit.

Several sources familiar with the investigation later shared shocking news about the DNA testing: Farwell was, in fact, not the father of Birchmore’s child. Farwell remains in the custody of the United States Marshals Service and has pleaded not guilty.

For now, no trial date has been set for Farwell, but as Friday’s “Dateline” episode showed, something went seriously awry in the investigation into Birchmore’s death. With all the evidence that has accumulated since the initial report, there was undeniably “a failure in many areas,” as McNamara put it in a “Dateline” interview.

For Boston.com’s full timeline of the Birchmore case up to September 2024, keep reading here.

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