A federal jury convicted Matthew Farwell, 41, on Tuesday of killing Sandra Birchmore and causing the death of her unborn child, according to The Boston Globe.

Jurors deliberated more than 15 hours over three days — and at one point reported a temporary deadlock — before finding him guilty on both counts.

Farwell faces an automatic mandatory sentence of life in prison without parole, with sentencing set for Feb. 3, 2027, and he will remain in federal custody until then.

U.S. Attorney Leah B. Foley told reporters, "Today, justice was served for Ms. Sandra Birchmore and her unborn son," calling his conduct "absolutely diabolical behavior."

Birchmore's family gasped as the verdict was read, per CBS News, and her cousin Ray Cosgrove said, "Sandra mattered before anyone outside her family knew her name."

What makes this outcome startling is that the case was officially closed twice before a jury ever heard it. No state charges were ever brought.

The FBI reopened the case in 2023, partly at the urging of a former Stoughton deputy chief who had run an internal affairs investigation, and concluded the local probe was rushed and compromised: Farwell was interviewed for only 15 minutes in a parking lot, without notes, injury checks or DNA sampling, and police examined his phone only after he had deleted texts with Birchmore, per CNN.

FBI Boston special agent in charge Ted Docks said, "No badge, no title, no position places anyone above the law."

The case reached a jury only through an unusual federal route.

Instead of a standard state murder charge, prosecutors charged Farwell with "killing a victim or witness," which required proving not only that he killed Birchmore intentionally, but that he did so to cover up federal crimes: sexually exploiting her while she was underage, using his police position to violate her rights, and defrauding the Stoughton Police Department by having sex with her while on the clock, The Boston Globe reports.

He was not charged with those underlying crimes individually, so prosecutors Elizabeth Riley, Brian Fogerty and Torey Cummings had to convince jurors of his implication in each.

A digital forensics expert testified that Birchmore's phone — described at trial as her "third arm" — stopped moving three minutes before surveillance video showed Farwell leaving her building, per CNN.

Birchmore met Farwell through the Stoughton Police Department's youth explorers program as a child cadet, and prosecutors said he began a sexual relationship with her when she was 15 and he was 27 — statutory rape under Massachusetts law, aggravated by his role as a mandated reporter.

The FBI investigation recovered roughly 40,000 texts between the two, including some reminiscing about sex while she was underage, according to CNN.

Prosecutors said Birchmore pressured Farwell to get her pregnant, became pregnant in late 2020, and that he turned furious when she said the baby was his. Twelve days before her death, a friend called Stoughton police dispatch to report the affair.

Prosecutors said that is when he decided to kill her — one day before his wife was scheduled to give birth, after which, per Oxygen's reporting on Foley's remarks, he drove to the hospital for the birth of his third child.

Farwell's court-appointed attorneys acknowledged the affair but argued Birchmore, who had a history of mental-health struggles and prior suicide threats, took her own life after he went to her apartment to end the relationship.

Defense attorney Kimberly Stevens asked jurors, "When all is lost and all hope is gone and you're alone in the world, are you going to pick your phone up?" per NBC Boston.

Prosecutor-hired expert Dr. William Smock testified her injuries showed strangulation with a duffel bag strap and a struggle, while defense expert Dr. Thomas Andrew, New Hampshire's former chief medical examiner, dismissed that homicide determination, NBC Boston reports.

Prosecutors leaned on Birchmore's own prolific texting to scaffold the trial, and family members told the jury through testimony that she was thrilled about motherhood — a boxed stroller and an ultrasound photo on the refrigerator were found in her apartment.

The verdict answers one question but leaves others open. Norfolk DA Michael Morrissey, who did not seek reelection amid criticism of his office's handling of the case, said in a statement that its ability to prosecute "was constrained" by the medical examiner's suicide finding, per CBS News.

U.S. Attorney Foley declined to comment on the state investigation, saying only, "The charges we brought were the ones we were able to charge."

Birchmore's cousin Barbara Wright said Farwell "can never hurt another human being again," but added, "There are still other people that we need to hold accountable. People who enabled him. People who [looked] the other way."

Stoughton Chief Donna McNamara said enough people "would not remain silent," and DA-elect Djuna Perkins, per Boston 25 News, is inheriting the fallout as her office charts a path forward.