Much of the federal trial of Matthew Farwell comes down to a scientific argument about a neck. Farwell, 40, a former Stoughton police detective, is accused of strangling Sandra Birchmore, 23, on Feb. 1, 2021, inside her Canton apartment and staging the scene to look like a suicide. He has pleaded not guilty and says Birchmore, who was pregnant, killed herself. On Tuesday, prosecutors put on Dr. William Smock, an independent medical examiner — a former assistant medical examiner in Kentucky and emergency room physician — who reviewed the case in June 2024 at the request of the FBI and the US Attorney’s office. His job, essentially, was to grade the first investigation’s homework, and as the Boston Globe reported from the courtroom, he found red flags everywhere.
One was in Birchmore’s hair, which was tangled in the material around her neck. “That’s a huge red flag for a forensic investigator,” Smock said. “One of the biggest red flags of a homicidal event is having the hair tangled up.”
Another was a snapped necklace with a flamingo pendant, found on Birchmore’s body. Smock spotted it in photographs taken inside her apartment — but State Police never logged it, and it was never provided to the state medical examiner’s office. Smock testified that he has never encountered a broken necklace on a victim of a suicidal hanging. (The gaps in the original State Police investigation are their own character in this trial; the defense leans on them, the prosecution has had to overcome them, and we’ve written about that problem before.)
Then there is the hyoid, a small U-shaped bone at the front of the neck. The bone is flexible in young people and typically doesn’t harden until around age 30, Smock testified. Birchmore was 23, and hers was fractured. “If it’s flexible, the chance of breaking it goes way down,” he said. A strangulation victim, though, can break a hyoid.
After lunch, Smock showed the jury a micro-CT scan of the bone he had commissioned to get a three-dimensional view. The imaging confirmed the bone wasn’t fused — and that the right side had broken inward. “This is a strangulation-related injury where the bone is squeezed inward,” he told the jury.
The bleeding pattern told a similar story. Dr. Maria Del Mar Capo-Martinez, who autopsied Birchmore for the state Office of the Chief Medical Examiner, documented petechial hemorrhages — bleeding from capillaries — in Birchmore’s larynx. In asphyxia cases, Smock testified, such hemorrhages develop above the point where pressure cut off the air supply. Birchmore’s were below where the duffel bag strap around her neck was found — positioned, he noted, between her voice box and her sternothyroid muscle. The implication, though Smock didn’t need to spell it out, is that whatever caused the bleeding wasn’t the strap.
Smock also pointed to abrasions on Birchmore’s nose, which he described as signs that pressure had been applied there, and to abrasions on her neck “consistent with fingernail marks.” Photographs of how her body was found on Feb. 4, 2021, suggested a partial hanging, he said.
All of this matters more than it otherwise might because the state’s own science has moved. The state medical examiner ruled Birchmore’s death a suicide in 2021, a ruling Farwell’s defense cites constantly. In April, the office withdrew that ruling; it now considers the manner of death medically undetermined. We’ve covered the trial’s competing accounts from the start.
The brother
Before Smock took the stand, the jury heard again from William Farwell, the defendant’s fraternal twin, testifying under an immunity agreement with the federal government: so long as he is truthful, he won’t be prosecuted for having sex with Birchmore while on duty as a Stoughton police officer. He had told the jury Friday that he began a consensual sexual relationship with Birchmore in 2018, when she was 21.
On Tuesday, prosecutor Brian Fogerty walked him through text messages from May 2019 in which William Farwell pressed Birchmore on when she and Matthew Farwell first had sex. “His house on April 10 many years ago,” she wrote — the same date she’d given for a first sexual encounter in 2013. Pushed further, she answered: “I was 15.” William Farwell’s reply, by text: “Nice.” Asked why he wrote that, he gave two reasons. “The first reason was I didn’t necessarily believe her.” The other: “I didn’t think my brother was that dumb.”
William Farwell also described his interview with State Police investigators days after Birchmore’s body was found. Lt. John Fanning, then a sergeant, and Trooper Matthew Dunne met him in a parking lot. Of the investigation, Fanning said, “I need this like I need a (expletive) bullet in the head,” and, “We’re getting a lot of calls and we need … to get this closed out,” Farwell testified — adding that he knew people had been posting Fanning’s phone number on social media. Fanning said he wasn’t there to investigate people’s marriages. “I have my own problems,” he said, per Farwell. David Linton, a spokesman for Norfolk District Attorney Michael Morrissey, declined to comment — “The NDAO cannot comment on an ongoing case” — and State Police did not immediately respond to an inquiry.
Then came the phones. Within a couple of months of Birchmore’s death, Matthew Farwell told his brother that State Police had “dumped his phones” — but that he had “wiped them” first. William Farwell recalled asking, “Did you Tom Brady that (expletive)?” — a Deflategate reference, he explained, to Brady allegedly destroying his phones rather than handing them to investigators. The brothers laughed about it, he said.
At some point after her death, William Farwell testified, he asked his brother directly: “Matty, tell me you didn’t (expletive) that girl when she was under 16.” Matthew Farwell said he did not. Later, Matthew told him the criminal investigation into Birchmore’s death had wrapped up — without saying how he knew. “There could have been serious charges,” Matthew Farwell said, according to his brother.
The last time William Farwell saw Birchmore was just after midnight on Jan. 10, 2021; texts showed he asked to come over for sex after a night of heavy drinking. He testified that he drove there drunk to the point of blacking out and has no memory of what happened in her apartment. On cross-examination, defense attorney Kimberly Stevens pressed him on the immunity deal and suggested he was upset with his brother; he denied it. He stepped down around 11 a.m.
Prosecutors’ theory is that Matthew Farwell killed Birchmore to stop her from disclosing his alleged federal crimes — including aggravated statutory rape, beginning, they say, when she was a 15-year-old in the Stoughton police Explorers program and he was a 27-year-old officer and her instructor. Birchmore’s estate has named both twins in a wrongful-death lawsuit; they deny wrongdoing.
The strangest exhibit in this trial remains the arc of the official record: a death ruled suicide, then un-ruled, then re-examined by an outside expert with a CT scan the first investigation never commissioned. The jury will have to decide whether a flexible 23-year-old bone breaks inward by itself.