MINNEAPOLIS (WCCO) – The Anoka County Sheriff's Office says a juvenile male entered Andover High School after hours on Monday and assaulted a female student in the school library.

The suspect is not a student of Andover, and it is not known what provoked the attack.

Law enforcement believes he gained entry into the school as another person left the building. He approached a female and allegedly punched her in the head before kicking her several times.

A teacher who was nearby intervened and was able to restrain the suspect until police could arrive. That teacher was also head-butted and kicked as a result.

The suspect allegedly claimed to have a knife, and threatened to kill other teachers. A knife was never found.

He is now in custody at the Lino Lakes Juvenile Detention Center. Police have charged him with fifth-degree assault and disorderly conduct, as well as trespassing. Additional charges are pending.

The victim was treated by paramedics and released to a parent. The teacher did not report any injuries from the assault.

The investigation is ongoing.