Authorities say the victim, 20, was walking onto the SEPTA platform at 1100 Market Street in Center City at 6 p.m. on Dec. 12 when an unknown suspect stole his wallet and fled onto a train.
The victim gave chase, but when he boarded the train, a large group of passengers assaulted him, police said. The extent of the victim's injuries were not immediately clear.
The mugging suspect is described as a black man wearing a black ski mask, a black sweatshirt, a blue hoodie, black pants, and black sneakers.
To submit an anonymous tip, call 215-686-8477 or visit PhillyPolice.com.
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