The incident happened on Lerner Court on July 21.
The video shows the suspect, identified by police as 36-year-old Jamal Gadson, walking by a 78-year-old woman.
After he passes her he stops, turns around, then pulls a knife and holds it to the woman's neck.
He then grabs the purse and runs off.
Gadson was arrested on Friday and faces numerous charges.
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