Authorities are investigating whether an MBTA Transit Police officer wounded during the shoot-out with the Boston Marathon bombing suspects was hit by friendly fire, State Police spokesman David Procopio confirmed Thursday.

Richard Donohue Jr., 33, was struck in the leg by a bullet, which authorities said remained embedded there. He was listed in serious but stable condition Thursday night at Mount Auburn Hospital in Cambridge.

“There is nothing conclusive at this time,’’ said a law enforcement source, who asked not to be identified but is familiar with the investigation. “There has been no forensics done. The doctors will have to determine when and if to remove the slug.’’


Another law enforcement official said authorities suspected that Donohue was hurt by friendly fire because of the positioning of police at the chaotic scene in Watertown last Friday morning.

“It was the fog of war,’’ the official said. “There’s usually one cop and one suspect. This is unprecedented.’’

A neighborhood resident, who said she saw Donohue fall as she watched from the window of her home, said in an interview Thursday she was immediately concerned that Donohue and other police officers were in the line of fire of fellow officers.

“There were bullets flying all around,’’ said the witness, who asked not to be named. “There was concern about officers being in harm’s way. It was a war out there.’’

The second law enforcement official said that whether Donohue was hit by friendly fire or not, officers were involved in a chaotic scene where they were trying to subdue a dangerous suspect. The suspect was shooting at police, and police were trying to protect themselves and each other by firing back, officials said.

“It doesn’t change anything at the scene, friendly fire or not,’’ the official said. “These suspects set in motion a chain of events that required this kind of response.’’


State Police investigators have recovered more than 250 shell casings as they try to determine the sequence, direction, and source of the gunfire during the shoot-out. They also recovered several homemade explosive devices, including a pressure-cooker bomb that detonated on the side of a parked car.

“Those streets in Watertown were the most complex crime scene in the history of the Massachusetts State Police,’’ Procopio said.