Police say 23-year-old Darnell Still is being sought in connection with the shooting on July 15 at Broad and Chestnut streets, just a block south of City Hall.
There were more than a dozen passengers on the bus when the gunfire rang out.
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A 29-year-old passenger was critically injured after being shot.
On Wednesday during a gun violence briefing, police released video of the suspect fleeing the bus as a flurry of people followed behind him, running for safety.
Anyone with any information on Still's whereabouts is asked to call police at 215-686-TIPS.