Three Stoughton police officers had inappropriate relationships with a young woman who killed herself last year while she was expecting her first child, according to a police internal affairs report released Friday, sometimes texting the woman while on duty to arrange meetings.

At the time of her death, Sandra Birchmore, 23, had been telling friends she was pregnant with the child of one of the officers, Matthew G. Farwell, 36, a detective, former patrolmen’s union president, and married father. They met when Birchmore was just 13 through the department’s youth explorers program, which introduces young people to law enforcement careers.

The redacted 60-page report offered the most detailed account to date of Birchmore’s relationships with Farwell, his twin brother, William, and their former supervisor in the department’s police explorers program, which ended in 2016.

All three officers have already left the police department. But, Police Chief Donna McNamara said she plans to ask the state’s new Peace Officer Standards and Training (POST) Commission to decertify Matthew and William Farwell as well as Officer Robert C. Devine as police officers. Under state law, law enforcement agencies in Massachusetts are prohibited from hiring decertified officers.

McNamara will also ask to have their names entered into a national database of decertified officers.

“I am seeking decertification for them because they all violated the oath of office and they should never have the privilege of serving a community as a police officer again,” said McNamara in an interview Thursday evening. “It’s the worst behavior I’ve ever seen.”

At a Friday morning news conference, McNamara struck a solemn tone, saying members of the town’s embattled force share her “anger and outrage” over the internal affairs report.

“These men violated their oath and they’re unfit to serve as police officers,” she told reporters at police headquarters. “I stand before you today as a civil servant who is heartbroken and incensed by what has transpired, and who pledges that this chapter in the Stoughton Police Department and the town of Stoughton is over.”

McNamara said Matthew Farwell embarked on an inappropriate relationship with Birchmore when she was 15 and he was 27, but declined to reveal specifics. However, three of Birchmore’s friends have told the Globe in a story that was published in April that Matthew Farwell began having sex with Birchmore when she was 15. If true, those actions would be statutory rape, as the age of consent in Massachusetts is 16.

In the report, author Stoughton Deputy Police Chief Brian J. Holmes wrote the relationship “continued for many years and included interactions and communications while Farwell was on duty for the Stoughton Police Department.”

McNamara said she is sorry that Birchmore “was failed so consistently throughout her life by three members of the Stoughton Police Department.”

“I‘m sorry these men saw fit to take advantage of her. And I’m sorry that we didn’t know more about this sooner” said McNamara, who has been chief since 2017.

A lawyer for Matthew Farwell said he hadn’t seen the report and couldn’t comment.

The investigation found the Farwell brothers both engaged in “conduct unbecoming of an officer” in their interactions with Birchmore and were untruthful with State Police who investigated her death about the extent of their relationships with her. It concluded the brothers showed incompetence and failed in their “attention and devotion to duty” in communications they had with Birchmore while on the clock as Stoughton officers.

The investigation also concluded that William Farwell improperly ran his and Birchmore’s names through law enforcement databases and violated another policy by coercing Birchmore via text message, though the specifics of the offense were redacted from the report. He didn’t respond Thursday to request for comment.

The investigation also concluded that Devine’s assertions that he had no contact or relationship with Birchmore were untrue, citing communications exchanged between the two on Facebook messenger. He also violated department rules by going to a restaurant in December 2020 to meet her while on duty, the report said.

In an e-mail, Devine denied the allegations.

“I will challenge these findings in every forum available to me and anticipate legal action for multiple infractions,” Devine wrote. “At least in my case, this was a politically motivated sham against an employee who has consistently spoken out against leadership. It speaks volumes that they released any findings to the media before ever notifying me.”

The department placed Matthew Farwell on paid administrative leave shortly after Birchmore died, and he resigned on April 1.

A separate investigation into Birchmore’s death by the office of Norfolk District Attorney Michael W. Morrissey concluded she took her own life. No criminal charges were filed, but Morrissey’s office referred information about its findings to Stoughton police for an internal affairs investigation. Now, the internal affairs report will be referred back to Morrissey’s office.

Birchmore’s death certificate shows she was pregnant when she died, but does not identify the baby’s father. In an interview with State Police investigators on Feb. 6, 2021, two days after Birchmore was found dead, Matthew Farwell acknowledged having sex with Birchmore in 2020, but said the sexual relationship ended that October. Birchmore said the baby was due in September 2021, Farwell told State Police, and based on that timeline, he was not the father.

The findings are the latest black mark for the department, which has weathered state and federal prosecutions of its officers, including the convictions of a previous chief and a sergeant in an extortion scheme.

Birchmore cherished Stoughton police’s explorers program and it was a major influence during her adolescence. Her father was never a part of her life, friends say, and her mother and grandmother — both of whom raised her — died when she was a teenager.

But as a Stoughton police explorer, Birchmore wrote on Facebook that she found an “amazing program” that teaches self-discipline and teamwork. In 2019, she took the Massachusetts civil service exam and was placed on the eligibility list for the Stoughton police force, records show.

William Farwell resigned from the department on Aug. 1, the same day he began a job with the Transportation Security Administration at Baltimore/Washington International Airport, where he is an explosives specialist. Last month, TSA spokesman said Farwell’s “pre-appointment review” “developed no derogatory information.”

In his resignation letter, William Farwell wrote that he denies “any/all allegations of misconduct,” adding, “I do not have confidence in the independence and objectivity of [the] town’s investigation and haven [sic] already provided at [sic] statement to the state police.”

Devine, 50, who joined the department in 1999, retired from the force, effective Aug. 16. During his career, Devine rose to the rank of deputy chief, but was demoted six years ago to patrol officer after an internal investigation found he lied to investigators looking into allegations that he improperly directed a subordinate to investigate a woman who was harassing him. He and the woman had had an extramarital affair, according to a report on that investigation.

In an August letter to McNamara, Devine, who is also a lawyer, criticized the internal investigation initiated after Birchmore’s death, writing that he was “unnecessarily and unfairly placed on leave in April as a political response to a news article.”

He said he had no “personal relationship” with Birchmore, didn’t socialize with her, didn’t share his phone number with her.

“Should you try to defame me at the end of this,” Devine wrote to McNamara, “I am prepared to resort to every legal means at my disposal to fight you.”

A friend and a co-worker of Birchmore have told the Globe they sent electronic messages to Birchmore shortly before she died, but she never responded. Police found Birchmore’s body in her apartment on Feb. 4, 2021, while conducting a well-being check sought by her employer, Sharon Public Schools, which had alerted authorities after she missed a few days of work. In the weeks before her death, Birchmore had received a $200 baby stroller as a gift and police found a sonogram photo in her kitchenette.

The internal affairs report said Matthew Farwell was the last known person to see Birchmore alive.

In his State Police interview, Matthew Farwell acknowledged visiting Birchmore’s apartment shortly before her death, saying he went there to end their relationship and deleted all his communications with her after he left. He told troopers he met Birchmore when she was a participant in the explorers program and he was an instructor, and knew about the challenges she faced at home.

“Matt said that Sandra had a troubled life and he felt bad for her. He would keep tabs on her over the years,” a State Police report said.

The internal affairs report said that Devine’s personnel file includes a 2014 letter from Birchmore’s mother, extending thanks to the department for the explorers program. A second letter, which was not signed or dated, was titled “My Hero Lieutenant Devine,” and discusses what he does for the community.

Deputy Chief Holmes wrote that he included the letters in the investigation as evidence that “exemplify both the public trust that was violated and what the Stoughton Police Explorers Class was supposed to be.”

Laura Crimaldi can be reached at laura.crimaldi@globe.com. Follow her on Twitter @lauracrimaldi. Dugan Arnett can be reached at dugan.arnett@globe.com.

Work at Boston Globe Media