Federal prosecutors presented new evidence in the case against Matthew Farwell, 39, who has been federally charged with the murder of his pregnant mistress, Sandra Birchmore, who was killed in February 2021. The former Massachusetts police officer is currently behind bars on charges of killing a pregnant witness or victim, and prosecutors intend to keep him there.

Abuse of Power

Prosecutors allege that Farwell committed the murder to conceal the affair with the 23-year-old. They say the victim was only 15 when Farwell initiated sexual contact. At the time, he served as an officer with the Stoughton Police Department, and Birchmore was a part of the youth program. 

“Farwell raped Birchmore as a child, continued to have sex with her when she became an adult, believed she was pregnant with his child, and killed her on Feb. 1, 2021, staging the crime scene to make it look like Birchmore committed suicide,” prosecutors wrote in a filing on Monday.

DNA Evidence

The new filing comes after Farwell filed his most recent petition to be released ahead of trial. Federal prosecutors are opposing his release, claiming his arguments are not substantial. In his petition, the defendant challenged most of the evidence. He argued that the DNA found under Birchmore’s nails did not match his, and his DNA also proved he was not the father of the unborn baby. 

“While Farwell correctly states in his memorandum that his DNA was not found under Birchmore’s fingernails, he fails to mention that Farwell’s DNA was found on the ligature that tied Birchmore’s neck to a closet door handle,” prosecutors said. “The presence of Farwell’s DNA on the murder weapon — i.e., the strap used to asphyxiate Birchmore — is, of course, highly inculpatory.”

Prosecutors also say they found Farwell’s DNA in the underwear Birchmore was wearing when her body was discovered, in multiple locations. Given that, prosecutors believe he lied to the Massachusetts State Police about having sex with Birchmore in October 2020.

To further their argument, prosecutors presented new evidence that proves Birchmore’s murder was premeditated. In the weeks leading up to her death, there were text messages on her phone that showed she “had a plan to obtain Farwell’s financial support for the child they both believed he fathered. And those communications indicate that Birchmore was willing to use her role as a victim of Farwell’s crimes to ensure that she and her unborn child would be financially secure.”

Coworkers Witnessed Change

The FBI spoke with former co-workers at the Stoughton Police Department, who claimed they noticed a change in his behavior at the beginning of 2021. They said he grew more stressed and just weeks before Birchmore’s murder, one coworker joined Farwell for lunch and said he looked stressed.

Prosecutors alleged that Farwell confided that he was having relationship problems with another woman who was not his wife. “When this witness asked if they could help, Farwell said, ‘The problem was going to take care of itself,‘” prosecutors said.

After the murder, witnesses told the FBI they did not see any remorse from Farwell and one even noted that he joked about the woman’s death. Another disturbing instance showing lack of compassion occurred when he was drunk at a gathering. 

Two witnesses reported he “sat down under a doorknob and demonstrated the position in which Birchmore was found, assuring the skeptical witnesses that it was possible to commit suicide in that manner. At the time, it had not been publicly revealed that Birchmore was found hanging from a doorknob.”

If he is convicted of the atrocious murder, he could face life in prison. His trial is currently set to begin on October 5, 2026.