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Twin of accused ex-officer testifies about relationship with Sandra Birchmore
William Farwell told a federal jury he had a sexual relationship with Birchmore when she was 20 or 21 and acknowledged he could face criminal charges for sex while on duty. His testimony came as prosecutors presented evidence in the murder case against his twin brother, Matthew Farwell.
BOSTON — William Farwell, a former Stoughton police officer, testified Monday that he had a sexual relationship with Sandra Birchmore while he was on duty. He said Birchmore was between 20 and 21 at the time.
Farwell was testifying at the federal murder trial of his twin brother, Matthew Farwell, who is accused of killing Birchmore and her unborn child and making her death appear to be a suicide. Matthew Farwell has pleaded not guilty. Prosecutors allege he began grooming Birchmore when she was 13 and began having sex with her when she was 15, while she was in the Stoughton Police Department’s Explorers program.
William Farwell told jurors he was testifying under a grant of immunity. He acknowledged that he could face a criminal charge for having sexual relations while serving as a police officer. He said he did not recall interacting with Birchmore before she turned 18, and that she later contacted him on Facebook Messenger for help reenlisting in the military after a medical discharge. He testified that they began a consensual relationship in the weeks that followed and met in their cars or at the home she shared with her aunt.
Farwell became a Stoughton officer in 2017. His police certification was permanently revoked in 2024 after an internal investigation found he had an inappropriate physical relationship with Birchmore and exchanged explicit messages and photos with her while on duty.
Earlier Monday, jurors heard from medical examiner Dr. Maria Capo Martinez, who initially ruled Birchmore’s 2021 death a suicide. Martinez testified that she was first told Birchmore had been found hanging by a scarf in her Canton apartment, with no signs of trauma and no suicide note. Prosecutors noted that Birchmore was found with a duffel-bag strap around her neck and pointed to autopsy images showing possible abrasions and a possible blunt-force injury to her chest.
Martinez said she was not shown certain evidence, including surveillance video, before finalizing her initial determination. After the FBI became involved and the case was reevaluated about two years later, she changed the death certificate: the cause remained asphyxia, but the manner of death was changed from suicide to undetermined.
William Farwell is expected to continue testifying Tuesday. Prosecutors could rest their case this week. Matthew Farwell faces a federal charge of killing a witness or victim and causing the death of an unborn child.