CLEVELAND: At least one other officer discharged a weapon during the final salvo fired by a Cleveland police officer who is on trial for voluntary manslaughter for shooting two unarmed suspects after a high-speed chase, a sound expert the defense hired testified Monday.

The sound expert said a dash-cam recording made by a suburban officer revealed that three other shots were fired during the four-second period when patrolman Michael Brelo, 31, stood on the hood of a beat-up car and fired his last 15 shots down through the windshield at the vehicle’s occupants.

Timothy Russell, 43, and Malissa Williams, 30, were killed in a 137-shot barrage of police gunfire Nov. 29, 2012, in the parking lot of a suburban elementary school where the chase ended.

The expert’s testimony helped solidify an argument that Brelo’s attorneys have long made: Brelo was not the only officer to fire at Russell’s Chevy Malibu during that final volley of gunfire.

Prosecutors have said that while 13 officers shot at the car that night, Brelo was the only one charged because he fired his last shots after the Malibu had stopped and the two were no longer a threat to officers’ lives.

Two of the prosecutor’s sound experts also said they found three other gunshots distinct from Brelo’s when reviewing the dash-cam recording.

Monday marked the fourth week of trial and the first day of direct testimony for Brelo’s defense. At Brelo’s request, a judge — not a jury — will decide the charges. Testimony is expected to conclude Thursday.

An optometrist and former police officer testified Monday that Brelo likely suffered from “tunnel vision” when he fired into the Malibu’s windshield and that earlier police radio traffic about weapons inside the Malibu and shots being fired in the parking lot would have led Brelo to believe that Russell and Williams were armed as he and other officers told investigators.

The optometrist acknowledged during cross-examination that he didn’t give Brelo an eye test and that Brelo never told investigators his vision was impaired during the shooting.

Brelo also said he could not remember standing on the hood of the Malibu, which his attorneys have not disputed.

Despite an exhaustive search by investigators, including a dive team, no gun was ever found.