BOSTON — Testimony in Matthew Farwell’s federal murder trial on Wednesday focused on the early investigation into Sandra Birchmore’s death, including what investigators documented, which evidence they collected and how they questioned Farwell, a former Stoughton police detective. State Trooper Matthew Dunne testified that he interviewed Farwell in an elementary school parking lot in the days after Birchmore died. The conversation was not recorded, and Dunne said he did not take notes. “We wanted to make sure we got a statement out of him, whether truthful or otherwise,” he told the jury. On cross-examination, Dunne said Farwell acknowledged visiting Birchmore’s Canton apartment the night she died. Farwell said he went to end their relationship and tell her the child she was carrying was not his, according to Dunne’s testimony. Birchmore had told others Farwell was the father, prosecutors say. Prosecutors also questioned Dunne about evidence and leads that were not pursued at the time. He testified that investigators did not notice a broken necklace with a flamingo pendant on Birchmore’s body and did not seize a duffel bag they believed might be connected to the strap from which she was found hanging. Dunne said troopers did not immediately seek to interview Farwell after Birchmore’s colleagues told investigators she was pregnant and identified Farwell as the father. Farwell, 40, is charged with killing Birchmore, who was 23 and 8 to 10 weeks pregnant when she died in February 2021, and causing the death of her fetus. Prosecutors allege he strangled her and staged her death to appear to be a suicide. He has been held without bail since his arrest in 2024. The defense questioned Dunne about Birchmore’s mental health and the condition of her apartment. Dunne said colleagues had reported that Birchmore discussed anxiety and possible depression; a relative told investigators she had been diagnosed with bipolar disorder and had experienced crises that included suicidal statements and hospitalization. Dunne also testified that he saw no signs of forced entry or a struggle in the apartment. The case has drawn scrutiny over the initial handling of Birchmore’s death. The state medical examiner first ruled it a suicide, and the Norfolk district attorney declined to bring charges. The examiner later changed the manner of death to undetermined. A medical examiner working with federal authorities concluded that Birchmore’s injuries were inconsistent with suicide and instead indicated strangulation, according to the case background presented in court coverage. To convict Farwell of Birchmore’s death, prosecutors must prove he killed her to prevent her from reporting that he had committed a crime. If convicted, he could face life in prison. The charges remain allegations, and the jury will decide whether prosecutors have proved them beyond a reasonable doubt.