Police said they arrested one suspect on Thursday tied to the brutal beating of a teen girl in a Brooklyn McDonald's.

The unidentified 16-year-old girl in custody reportedly already had a long record that included six arrests — at least one for stabbing her brother and another for assaulting her grandmother.

Chief of Detectives Robert Boyce told reporters investigators were looking for five more people seen on the video, and that they did not yet know the fight’s cause.

No charges were filed as of Thursday afternoon and police said the investigation was ongoing.

The three-minute video of Monday's fast food fist fight melee at a McDonald's on Flatbush Avenue went viral soon after it was uploaded on Facebook. 

The group of teenage girls thought to attend the nearby by Erasmus Hall High School are seen walloping a 15-year-old classmate.

The victim, whose name has not been released and seemed to lose consciousness before one attacker stomped on her head, was eventually dragged onto a bench and laid down by a group of witnesses.

Police said nobody in the crowd called for help, despite many of them caught on cell phone cameras using their own phones to record the fight.

NYPD Commissioner Bill Bratton told reporters cops would work closely with the Brooklyn DA's office to track the assailants down.

"That type of behavior is not acceptable in any society, and certainly is not going to be acceptable here in New York," he said.