Echoing the account of Trombly and several prosecution witnesses, Byrne acknowledged that he replied with a string of profanity strewn insults, but adamantly maintained that he drew the line at insulting Trombly’s mother, as the prosecution claimed he had.

In cross-examination, Assistant United States Attorney S. Theodore Merritt ’74 called Byrne’s version of the night into question, noting that the sergeant and his lawyers had never offered this story before last week.

The sergeant denied the prosecutor's charge that he instructed several subordinate BPD officers to mislead investigators. Byrne said that after hearing of Trombly’s claim that the officer had broken his jaw—a story which he said he thought was false at the time—he reassured the officers and advised them against spreading rumors. He insisted that he never told them to lie.

Byrne also disputed the claim of several witnesses that he had berated a friend of Trombly’s immediately before his arrest, saying that his attitude towards the woman was “stern” but “fatherly.”

In addition to Trombly, prosecution witnesses in the case have included two BC students who attended the parties on the nights in question, as well as a close friend arrested along with Trombly who testified that he witnessed part of the alleged beating.

On Thursday, the prosecution called Cynthia G. McGinn, the emergency room doctor who diagnosed Trombly as having a displaced jaw fracture the morning after the alleged incident. McGinn, who is also an instructor at Harvard Medical School, said the injury was consistent with a substantial impact, comparing it to the damage done by a car accident.

Prosecutors have also called a number of BPD officers who witnessed parts of the evening of Trombly’s arrest or were involved in the investigation of the incident—several of whom spoke under compulsion orders and immunity agreements. On Friday, a BPD lieutenant who was present in the station house at the time testified for the defense.

Testimony in the trial, which began with jury selection Aug. 25, is expected to wrap up with a final defense witness this morning.

If convicted, Byrne faces up to 10 years in jail and a fine of up to $250,000 for the civil rights charge, as well as up to 10 years in jail and a fine of up to $250,000 for each of the four counts of witness tampering.

—Staff writer Simon W. Vozick-Levinson can be reached at vozick@fas.harvard.edu.