A Massachusetts prosecutor says it's "highly likely" a police officer was critically injured by friendly fire during a gun battle with the Boston Marathon bombers in April 2013.

But Middlesex District Attorney Marian Ryan said Tuesday that whatever wounded MBTA Officer Richard Donohue is still in the officer's body and can't be examined to confirm. Her office's report concluded the gunfire was justified.

The gunfight took place days after bombs exploded at the marathon, killing three people and injuring over 260.

One of bombers, Tamerlan Tsarnaev, was killed. His brother, Dzhokhar (joh-HAHR'), was eventually captured. He was sentenced to death last month.

The Massachusetts Emergency Management Agency concluded in a separate report that officers showed a lack of "weapons discipline," resulting in dangerous crossfire.