The murder trial of a former Massachusetts police officer accused of killing his pregnant mistress and disguising the death as a suicide is set to begin following a brief hearing at 9 a.m. Friday.

After the jury is seated, attorneys are expected to deliver opening statements. Testimony will then begin with Stoughton Detective Heather Cheever, followed by a local elementary school official.

The FBI arrested former Stoughton Police Officer Matthew Farwell, 40, in August 2024 over the death of 23-year-old Sandra Birchmore, who died three years earlier.

Prosecutors allege that Farwell groomed Birchmore beginning when she was a teenager, maintained a sexual relationship with her for years and killed her after she disclosed that she was pregnant. They also accuse him of staging the scene to make her death appear to be a suicide.

Birchmore’s death was initially ruled a suicide. Farwell was later charged after investigations by the department’s internal affairs unit and the FBI.

Federal prosecutors alleged last year that Farwell killed Birchmore, who was pregnant, to stop her from speaking out after she told him she intended to “keep” the baby. According to prosecutors, he responded by telling her she was “the worst person on the face of the earth.”

Both sides have agreed that DNA testing ruled out Farwell as the father of Birchmore’s unborn child. Prosecutors nevertheless claim he believed he was the father, citing text messages exchanged with Birchmore from Dec. 28, 2020, through Feb. 1, 2021—the day she died.

According to prosecutors, Birchmore was enthusiastic about the pregnancy and kept Farwell informed about her due date, ultrasounds, medical appointments and a planned gender reveal.

She was between eight and 10 weeks pregnant when she died, about two weeks before Valentine’s Day. Prosecutors say she intended to announce the pregnancy publicly on that day.

Court documents say Birchmore was 12 when she joined the police department’s explorers program. Farwell volunteered with the program and is accused of using that position to groom, exploit and abuse her after she turned 15; he was 27 at the time.

Prosecutors allege the sexual relationship continued into Birchmore’s adulthood, including encounters while Farwell was on duty. He is accused of strangling her on Feb. 1, 2021, after learning she was pregnant.

Farwell has pleaded not guilty and has remained jailed since his August 2024 arrest.

Stoughton is located roughly 20 miles south of Boston.

Jury selection was completed earlier this week.