A Prince George’s County police officer caught on video beating an unarmed college student as he lay on the ground during a raucous celebration in College Park in 2010 initially told an investigator that he did not know who swung the baton, the investigator testified Tuesday.

In an April 2010 conversation with Lt. Charles Walls of Internal Affairs, Officer James Harrison said he “couldn’t actually identify himself” in video footage that shows two officers repeatedly striking University of Maryland student John McKenna, Walls testified.

Shown the video, Walls said, Harrison initially said he was “more in the middle of the line,” a short distance away from the beating.

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, which followed a U-Md. basketball 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 acting as “foot soldiers” trying to control a violent riot in College Park.

Walls’s testimony in Prince George’s County Circuit Court was key to prosecutors’ attempt to convince jurors that Harrison knew what he did was wrong and tried to cover up his conduct.

Another investigator testified that neither Harrison nor Baker completed a required “use of force” report after the incident, although the officers’ defense attorneys questioned whether that was necessary since a commander had filed a report authorizing lower-ranking officers to use chemical agents.

Walls testified that his unit was assigned the case in April 2010 and began asking the officers working that night if they knew who was shown on video footage, recorded by another student, that captured McKenna’s beating. In an interview at the Internal Affairs office in Clinton, Harrison said he could not, Walls testified.

Harrison called Walls the next day, the investigator testified, 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 was unclear how defense attorneys would address Walls’s testimony. In questioning the investigator, Harrison’s defense attorney David Simpson seemed to suggest that his client was nervous about being suspended or fired because of news reports he had seen.

Walls said that Harrison merely mentioned a news report about an officer’s suspension when asked if he had heard any rumors about the case.

Also on Tuesday, Sgt. Dexter McKinney, a friend of Baker’s who was 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.”

McKinney said that Baker fully acknowledged that he was the one on the video and said he was “sorry it happened” and was “just not feeling good about it.”

In their questioning of McKinney, defense attorneys suggested Baker was apologizing because his actions had thrust colleagues into an Internal Affairs investigation, not necessarily for his conduct after the game.

Defense attorneys might begin their case Wednesday after prosecutors finish questioning their expert witness on Baker and Harrison’s use of force. On Tuesday, that witness, Shannon Bohrer, a retired Maryland State Police sergeant, testified that he felt it was appropriate for Harrison and Baker to bring McKenna down with their shields and batons but that striking him after that was “excessive.”

“When he went to the ground, the force should have stopped,” Bohrer testified.

Defense attorneys forced Bohrer to acknowledge that police policies called for the officers to be judged from their own perspective, using the evidence available to them at the time of the incident. Although Bohrer called the force excessive, he agreed that the officers had been authorized to use chemical agents and that the alleged misdeeds with batons lasted mere seconds.