FBI Special Agent Heidi Kelsch, who led the investigation, said Birchmore’s devices contained about 40,000 messages between the two. Prosecutors presented exchanges describing sexual encounters, including messages in which Birchmore referred to an encounter in April 2013 as the best day of her life. Kelsch testified that Farwell was 27 and Birchmore was 15 at the time. Prosecutors say he groomed her and sexually abused her as a minor.

Kelsch said Birchmore’s unexcused absences from Stoughton High School rose from nine during her sophomore year to 19 during her junior year, with the increase occurring after May 2013. She also described messages indicating that the two had sex while Birchmore was supposed to be at school. Birchmore later died at 23, and was pregnant.

The agent testified that Farwell’s department-issued phone was searched eight days after Birchmore’s death and before it was turned over to investigators. The searches included questions about whether consent could be withdrawn in Massachusetts and whether deleted iMessages could be recovered, Kelsch said. Farwell’s devices did not contain messages with Birchmore, she testified, while Birchmore’s phone had multiple messages in which Farwell told her to delete their exchanges.

The prosecution alleges Farwell killed Birchmore and her unborn child in her Canton apartment on Feb. 1, 2021, then arranged the scene to make her death appear to be a suicide. Farwell’s lawyers argue that Birchmore died by suicide after he ended their relationship and told her he was not the father of her unborn child.

During cross-examination, FBI digital forensic examiner Christopher Beckstrom said Birchmore’s device showed searches about suicide ribbons around 7:50 p.m. on the night she died. He also testified that she had made a list of baby names on Jan. 27 that included the name Matthew.

Beckstrom said Birchmore’s laptop recorded a final user action at 9:10 p.m. involving a message between her and Farwell. Her phone locked three minutes later and recorded eight steps at 9:40 p.m. Farwell left the apartment building at about 9:43 p.m., according to testimony.

Kelsch said the FBI began investigating Farwell in October 2023 after receiving referrals from Brian Holmes, then Stoughton’s deputy police chief, and another law enforcement officer. Stoughton police did not investigate Birchmore’s death because it occurred in Canton, Chief Donna McNamara testified earlier in the trial, but the department opened an internal investigation into Farwell.

That internal report concluded that Farwell, his twin brother William Farwell and former Deputy Chief Robert Devine had inappropriate relationships with Birchmore. Farwell resigned from the department in April 2021. Birchmore had met him through Stoughton’s Police Explorer program when she was 12; the program was disbanded in September 2022.

Holmes testified that he first contacted the FBI in Lakeville in June 2022. He and McNamara said department rules prohibit officers from having sex while on duty. Prosecutors have cited the alleged on-duty conduct as part of their argument that Farwell exploited Birchmore and defrauded the town.

Testimony was scheduled to resume Monday.