A 55-year-old man waiting at a North Philadelphia bus stop on his way to work was killed early Tuesday in a shooting witnessed by a SEPTA driver and passengers on an arriving bus, police said.

Investigators are hoping video from the bus will help them identify the gunman in what was the last of three fatal shootings in Philadelphia overnight.

The shooting occurred about 2:40 a.m. at Sixth and Erie Streets, officials said.

Police said the man, whose name was not immediately released, struggled with the attacker before he was shot once in the head at close range. The victim was pronounced dead at the scene at 2:57 a.m.

Chief Inspector Scott Small told reporters that witnesses on a Route 56 bus, including two of the victim's co-workers, saw the struggle and heard the gun go off.

He said police are trying to determine if the shooting was an attempted robbery or involved some other motive.

In the other slayings overnight, a 32-year-old man was killed and a 28-year-old man was wounded in a shooting about 10:20 p.m. Monday on the 7700 block of Matthias Street in Roxborough, and a 20-year-old man was gunned down about 40 minutes later on the 3900 block of Dungan Street in Juniata Park, police said.

Neither homicide victim has been identified and no arrests have been reported.