It began after an 18-year-old student allegedly stole a cellphone from a younger one, multiple sources confirmed.
The alleged victim and a friend grabbed the older student and beat him in a school hallway after lunch this past Tuesday, the sources said.
The incident was captured on school surveillance cameras and student cellphone video, they said.
His assailants apparently didn't know that the older student had previously sustained a traumatic brain injury. He was brought to Hackensack University Medical Center as a precaution and reportedly checked out OK, the sources said.
Then he apparently took to social media to vent his frustrations.
Washington Township Police Chief Richard Skinner said his department, in consultation with the Bergen County Prosecutor's Office, didn't find the alleged threats credible.
Skinner and Westwood Police Chief Michael Pontillo nonetheless boosted police presence at the school this past week out of what Skinner said was "an abundance of caution."
The chief said he couldn't comment further because juveniles are involved.
School sources, however, said that none of them have been allowed to return to school just yet.
"The alleged actor of this threat will not be allowed in the school building," Acting Schools Supt. Jill Mortimer said in a message to the community. "We have several measures in place to prevent that from happening."
The increased police presence will continue "if deemed necessary," Mortimer said. "This will supplement the security measures we already have in place."
Delinquency complaints were expected to be signed against the two boys who allegedly jumped the older student. That case would be heard behind closed doors in the Family Part of Superior Court in Hackensack.
Police, meanwhile, are investigating the alleged phone theft. They and school officials are also monitoring social media.
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