Testimony to begin in trial of ex-Massachusetts police officer accused of killing Sandra Birchmore

Testimony is set to begin Tuesday in the trial of Matthew Farwell, the former Stoughton, Massachusetts police officer accused of killing Sandra Birchmore and her unborn baby.

Federal prosecutors said Farwell met Birchmore when she was 13 years old and a member of the police department's youth program. Investigators said he groomed Birchmore for years and began having sex with her when she was 15 and he was 27.

Birchmore was found dead at the age of 23 in her apartment in Canton in February 2021. Her death was initially ruled a suicide. Prosecutors said she was pregnant at the time with what she believed was Farwell's child.

"At that point, the only thing that we thought of is that Matthew Farwell murdered her," Lauren Andrews, the mother of one of Birchmore's closest friends, told CBS News. "It was complete one hundred percent exploitation is what it was. It was grooming and then the passing her around to other police officers."

Farwell's attorney did not deny her client and Birchmore had an affair, but she said Farwell never thought the baby was his and when he broke up with Birchmore, she killed herself. The defense said in a court filing that DNA testing confirmed Farwell was not the father.

The prosecution said Birchmore eventually started to realize Farwell's behavior was wrong and threatened to expose him unless he agreed to give her a baby.

"She could end his life with the information she had, so he was going to end hers first," prosecutor Torey Cummings said in opening statements Friday. The prosecution said Farwell strangled Birchmore on February 1, 2021 and staged it as a suicide.

Farwell is charged with one federal count of killing a witness or victim and faces a mandatory sentence of life in prison if convicted at his trial in South Boston. He also faces a charge of causing the death of an unborn child. He has pleaded not guilty to both.

"Matthew Farwell did not kill Sandra Birchmore. He did not," his attorney Kimberly Stevens said in opening statements.

Over the weekend, prosecutors filed a new motion asking that the jury hear about three other alleged affairs that Farwell, a married father of three, had. They claim the other affairs are evidence that Farwell took extra steps to hide his relationship with Birchmore.

Andrews said Birchmore was excited about becoming a mother.

"She made a really strong decision that she was going to go to nursing school, and she had applied to nursing school," Andrews told CBS News. "There is absolutely no way I can tell you from my heart that that woman was going to commit suicide."

A Stoughton police officer will be the first witness to take the stand Tuesday. Sixteen jurors - ten men and six women - have been seated for the trial, which is expected to last about five weeks.

No cameras are allowed in federal court so the trial is not being livestreamed or broadcast.