Federal prosecutors are asking a judge to let three women testify about alleged extramarital affairs with former Stoughton police officer Matthew Farwell, arguing their accounts could rebut his defense’s explanation for why he wore a mask when he visited Sandra Birchmore’s apartment on the night she died. In a motion filed Sunday, Oct. 11, prosecutors said the women would testify that Farwell did not disguise himself or otherwise try to conceal his encounters with them. They contend that evidence would counter the defense’s opening-statement argument that Farwell wore a mask at Birchmore’s Canton home on Feb. 1, 2021, to hide infidelity from his wife. Farwell’s lawyer, Kimberly Stevens, described the mask as evidence of an innocent effort to keep his wife from learning about cheating, according to prosecutors’ filing. Prosecutors argue the other women’s testimony would show that Farwell did not take similar precautions during those alleged affairs. The government previously sought to introduce limited evidence of at least three affairs, but the judge denied that request. Prosecutors say statements made by the defense during opening arguments Friday make the testimony newly relevant. The judge has not ruled on the latest motion, and the defense had not filed a response as of the report’s publication. Farwell is charged with killing Birchmore, who was pregnant, and making her 2021 death appear to be a suicide. Prosecutors allege he acted to prevent her from exposing sexual exploitation that began when she was 15. Farwell has pleaded not guilty; the allegations have not been proven in court. Prosecutors also filed a separate motion seeking instructions to the jury concerning what they characterize as legal misstatements and references to disputed exhibits during the defense’s opening statement. The court was scheduled to resume Tuesday, with the first witnesses expected to testify after jurors were dismissed Friday. Court was not in session Monday because of the holiday.