The gun apparently went off during a struggle on the train, and a bullet sailed through a train window and struck the man standing on the station platform. Police said they believe he had just gotten off the train when he was hit.

Police believe the group that included the attacker fled from the train at the Stadium station. The man and son who had been assaulted stayed on the train and met up with police at the Central West End station. They were treated at hospitals for facial injuries.

Authorities had surveillance video, but were not releasing it. They released a photo of someone they want to question. Warnecke was careful to not call the person in the photo a suspect, but stressed police want to question him.

The person pictured is about 16- to 19-years-old and black. He was wearing an orange coat, black pants and purple flip-flop style shoes and was carrying a purple Adidas bag. He was last seen at the Central West End MetroLink station.

"We think this individual may have some information as to who may have been on that train," Warnecke said.

Warnecke said there were no MetroLink employees or security officers on the train or on the platform when the shooting occurred.