Oakland police have opened an investigation into a group of men who were said to have restrained the teen driver accused of killing three people in a hit-and-run last weekend, after a newly emerged video showed them violently beating the boy before officers arrived, the Chronicle has learned.

The video, while chaotic and grainy, shows a group of about five men surrounding the 17-year-old as they take turns punching him. Someone is heard yelling “get on him” and another saying “sorry.” At one point the teenager is seen attempting to cover his face with his forearms.

The Chronicle confirmed the authenticity of the video and existence of the criminal probe through a law enforcement source who spoke on the condition of anonymity in accordance with the newspaper’s policies.

The teen was charged with manslaughter earlier this week, following a crash that injured several victims and killed three men identified as Miguel Angel Sanchez Ramirez, 44, Charles Ray Blackmon, 65, and Robert Dixon, 64. The investigation means that the juvenile, whose identity was not disclosed due to this age, will now be treated as both a suspect and a victim in the same incident.

The burst of apparent vigilante justice complicates a narrative put forth by Oakland leaders earlier this week, who praised the people who detained the teen as he allegedly tried to flee the scene.

“I have to say that the courage displayed by those on scene shows a growing trust between our neighborhoods, City Hall and the Oakland Police Department,” Mayor Barbara Lee said at a Monday press briefing. “We’re committed to working with OPD to ensure accountability and to support those impacted by this tragedy.”

Oakland Police Chief James Beere thanked the community members that he said “stepped up to assist, to help detain the suspect and prevent him from fleeing.”

When a reporter at the presser asked Beere about a video suggesting the suspect had himself been attacked, Beere said that “we’re going to look into everything.” Neither he nor Lee explicitly acknowledged seeing the video.

Officials with Oakland police and Lee’s office did not immediately respond to requests for comment Thursday.

The crash, also captured on video, occurred at about 11:15 p.m. Saturday, when a vehicle plowed into a group of people on a sidewalk near the intersection of 85th Avenue and International Boulevard.

Authorities said the teen had been driving recklessly at over 50 mph before he struck parked vehicles, went onto the sidewalk and rammed into those standing there.

Beere on Monday said the driver tried to flee the scene before he was restrained by bystanders. Investigators plan to analyze blood and toxicology reports to see whether the teen had alcohol or other drugs in his system.

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This article originally published at Men praised for detaining teen after fatal Oakland crash now investigated in his beating.