Farwell, who had pleaded not guilty, was charged with killing a witness or victim and causing the death of an unborn child. To convict him on the witness-killing charge, jurors had to find not only that he killed Birchmore but that he did so to stop her from reporting his crimes to federal authorities. The jury had signaled a day earlier that it was deadlocked before ultimately reaching a verdict.

Farwell now faces a mandatory sentence of life in prison without the possibility of parole. Sentencing is set for Feb. 3, 2027. The Department of Justice had the option of seeking the death penalty but announced last year that it would not.

The four-week trial featured testimony from 50 witnesses. Prosecutors argued that Farwell strangled Birchmore, who was pregnant with what she believed was his child, and then staged her death to look like a suicide to conceal a years-long affair. The defense contended that Birchmore had a history of mental health struggles and took her own life after Farwell told her he was not the father and that the relationship was over.

Birchmore, 23, was found dead in her Canton apartment in February 2021 with a strap hanging around her neck. Her death was initially ruled a suicide. More than three years later, Farwell was arrested and the medical examiner changed the manner of death to "undetermined."

Farwell and Birchmore met when she was a 13-year-old cadet in the Stoughton Police Department's youth explorers program. Prosecutors say Farwell began a sexual relationship with her when she was 15.

"Today, justice was served for Ms. Sandra Birchmore and her unborn son, both of whom died at the hands of Matthew Farwell. The evidence presented at trial was both shocking and clear," U.S. Attorney for Massachusetts Leah Foley said at a news conference, describing Farwell's actions as "absolutely diabolical behavior."

Outside court, Birchmore's cousin Barbara Wright described a mix of emotions. "It's been almost six years since we lost Sandra and let's not forget her baby boy," she said. "We finally got justice. We've been fighting long and hard for her. And she deserves it. She's waited a long time."

Norfolk District Attorney Michael Morrissey, whose office declined to pursue state charges against Farwell, said in a statement that he hopes the verdict brings closure to Birchmore's family and friends. The office has faced criticism from Birchmore's loved ones over that decision.

"The Norfolk District Attorney's Office recognizes the criticism it has received for its handling of this case. However, its ability to prosecute was constrained by the finding of the Office of the Chief Medical Examiner that the manner of death was suicide," Morrissey said. He noted that the office referred the case to the Attorney General's Office, worked collaboratively with federal prosecutors, and made its case file public beginning in October 2022. "We respect the jury's verdict and will have no further comments."

Acting Stoughton Police Chief James O'Connor said he fully supported the verdict. "It is the outcome Sandra, her unborn child, and her family have deserved for more than five years," he said. "What happened to Sandra is a profound betrayal of the trust every police officer is sworn to uphold. Matthew Farwell used his position to harm someone the community had put in the care of this department. He no longer wears this badge, and he does not represent the men and women of the Stoughton Police Department, who serve this town with honor every day."

Chief Donna McNamara, who is on paid leave from the department as part of an unrelated investigation, said the verdict was about honoring Birchmore. "Today is not just about a verdict. Today is about Sandra. Today a federal jury has confirmed what became apparent to me some time ago, that Sandra was murdered and that her murderer was a police officer who took advantage of her trust and faith in the badge and uniform," she said. "There are those who wanted to forget Sandra Birchmore. But enough people would not remain silent. Enough people spoke up. Enough people asked questions. And rest assured that there are still more questions unanswered than are answered, even after today."