It happened just before 9 p.m. Sunday near the 5300 block of Horrocks Street.
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New surveillance video shows the shooter waiting two minutes for 17-year-old Teryn Johnson to walk by late Sunday night.
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The gunman then shot Johnson in the chest before getting into a waiting Dodge Charger and fleeing the scene.
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The teen was rushed to Temple University Hospital where she later died.
Johnson was walking with another teenage girl at the time of the shooting but she was not injured.
A $20,000 reward is being offered for information leading to an arrest and conviction.
Anyone with information is asked to call police at 215-686-TIPS.