Police say the device was disguised to look like a flashlight.
When the suspect was arrested, officers say he was also armed with a knife.
A woman in the park tripped and injured herself while she was trying to get away from the man.
Police, local politicians and the community met Wednesday to address the crime and violence inside the park. A midnight curfew was put into place to help get control of the situation, but community members say many are ignoring curfew.
Cops meet with community about Washington Square Park parties
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