The thieves, investigators say, sneak into the lot and steal "three or four" vehicles, driving single-file to the toll booth at the lot's exit. There, the lead driver forces the booth operator to open the gate at gunpoint and the crew flees, according to police.
Authorities have released the footage from one such robbery that was caught on video.
The armed suspect in the police video is described as a black man in his early 20s wearing a black hoodie and a black face mask.
Anyone with information is urged to call 215-686-8477 or submit an anonymous tip on the PPD website.
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