WATCH: NYPD Questioning Five Suspects and Have Motive in Vicious Beating and Robbery of 15-Year-Old Brooklyn Girl

Police were questioning five suspects and have a motive in the vicious mob beating of a 15-year-old girl on a Brooklyn street, law enforcement sources said Friday.

Cops were grilling the teenage boys in Crown Heights Friday after a group of teens savagely attacked the girl Thursday — as retaliation for a fight she got into earlier in the day, according to the sources.

The caught-on-camera beating unfolded after the girl allegedly beat up another girl earlier in the day at school, according to the sources.

The group of teenage attackers were allegedly friends with the girl who the victim had tussled with, law enforcement sources said.

Stunning surveillance footage video shows the teens — many of them boys — storming the girl, jumping on her and stomping on her head as she lay helplessly on the sidewalk.

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SOURCE: New York Post, Larry Celona, Joe Marino, and Natalie O’Neill