UPDATE: Police have identified the victim and report that they have made an arrest. According to philly.com:
George Cobb was charged today with murder and related offenses in the death of Donald Mines, of the 1300 block of Wells Street in the Castor section.
Police said the victim was shot once in the chest at 4:19 p.m. and pronounced dead on the scene by medics a short time later. The victim’s name has not been released and no arrests were reported.