[There was a video here]

Philadelphia police are searching for a teenager caught on surveillance camera knocking a 60-year-old man out cold on the platform of a SEPTA train station Monday.

Police told Philly.com that the older man got into an argument with the teen inside a train headed for the 15th Street station Monday afternoon after he apparently stepped on the foot of the teen's friend standing just inside the doorway. The teen, wearing a blue hoodie, can be seen arguing with the man for some time inside the train; a group of teenage girls can also be seen trying to intervene.

Their argument continued onto the platform of the 15th Street station, where a group can be seen swarming around the teen and the man. The teen clocks the older man, who falls to the ground unconscious; the group almost immediately disperses. Police told NBC Philadelphia that the man suffered "concussion-like symptoms" and a broken jaw.

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