One of the Prince George’s County police officers caught on video beating an unarmed University of Maryland student as he lay on the ground during a raucous basketball postgame celebration in 2010 initially told an internal affairs investigator he was a witness to the incident and did not know who was on the footage swinging a baton, the investigator testified Tuesday.

In an April 2010 conversation with internal affairs Lt. Charles Walls, Officer James Harrison said he “couldn’t actually identify himself” in video footage that shows two officers repeatedly striking U-Md. student John McKenna, Walls testified Tuesday. As he was shown the video, Harrison said he was “more in the middle of the line,” a short distance away from the area where the beating took place, Walls testified.

Harrison and another Prince George’s officer, Reginald Baker, are facing first-degree assault and misconduct in office charges in connection with the March 2010 incident after U-Md.’s upset victory over Duke. Prosecutors have said they were the officers caught on tape slamming McKenna with a riot shield after he skipped toward them, then beating him with a baton after he crumpled to the ground.

Defense attorneys have argued that Harrison and Baker were merely doing their jobs, acting as “foot soldiers” trying to control a violent postgame riot in College Park. Walls’s testimony Tuesday at their trial in Prince George’s County Circuit Court was a key cog in prosecutors’ attempts to convince jurors that Harrison knew what he did was wrong and that he made some effort to cover up his conduct.

Walls testified that his unit was assigned the case in April 2010 and began asking all the officers working that night if they knew who was shown on video footage that captured McKenna’s beating. In an interview at the internal affairs office in Clinton, Harrison “said he was a witness” and could not identify those actually swinging their batons, Walls testified.

Walls testified that Harrison called him personally the next day and asked what equipment he would need to turn in, feeling his “suspension was imminent.” Even then, Walls testified, Harrison stopped short of admitting his role in the incident.

It remains unclear exactly how defense attorneys will combat Walls’s testimony. In questioning the investigator, David Simpson, Harrison’s defense attorney, seemed to suggest Harrison was nervous about being suspended or fired immediately because of news reports he had seen. Walls disputed that, saying Harrison merely brought up a news report about an officer’s suspension when Walls asked him if he had heard any rumors about the case.

Also Tuesday, Sgt. Dexter McKinney, a friend of Baker who was also working the night of the incident, testified that after he was interviewed by internal affairs detectives, Baker called him and “apologized for putting us through that.” Of the incident, McKinney said Baker acknowledged fully he was the one on the video and said he was “sorry it happened” and was “just not feeling good about it.”

“He wasn’t proud of it,” McKinney testified.

In their own questioning of McKinney, defense attorneys suggested Baker was apologizing not necessarily for his conduct that night but because his actions had thrust colleagues into an internal affairs investigation.

Testimony is scheduled to resume at 1:15 p.m. Tuesday and continue later into the week.