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.

HORRIFIC VIDEO: VICIOUS NEW YORK CITY MUGGING CAUGHT ON CAMERA

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.

One of the teens then snatched the Air Jordans off her feet before the group bolted, according to cops and the footage.

The victim was rushed to a hospital with head trauma and later released, officials said.

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The five boys turned themselves in with their parents earlier Friday, according to a law enforcement source. Their names and ages were not immediately clear and no charges have been filed as of early Saturday morning.

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