Guy Womack, who is serving as Sgt. Robert Richards' civilian attorney, said Richards regrets the incident and didn't know someone was videotaping it, Stars and Stripes reported.
"To urinate on their dead bodies was wrong," Womack said. "It's embarrassing to everyone."
However, he added that it was intended as "black humor" not desecration.
The incident caused an uproar after the video was posted on YouTube in 2012.
Following a daylong hearing at Camp Lejeune, N.C., an investigating officer must decide what charges, if any, Richards will face for the incident.
He is also suspected of failing to properly supervise fellow Marines and using weapons indiscriminately.
Lt. Col. Christopher Greer, the investigating officer in the case, is not expected to offer his recommendation until at least Friday, Stars and Stripes said.