STOCKTON, Calif. (AP) — A 15-year-old girl was stabbed to death Monday on a high school campus in an apparently random attack, authorities said.

The girl was stabbed several times at about 11 a.m. at Stagg High School in Stockton in California’s Central Valley and died at a hospital, Stockton Unified School District Superintendent John Ramirez Jr. said at a news conference.

Her name wasn’t immediately released.

The attacker, a man in his 40s, was quickly detained. His name was not released.

The man drove to the school and went through a campus gate, police said.

He attacked before security and staff could stop him, Ramirez said.

“We definitely will be re-evaluating” campus security, he said.

The school was placed on lockdown after the stabbing.

Police initially said the teenager appeared to have been targeted. But Officer Joe Silva told the Sacramento Bee on Monday evening that detectives now believe it was a random act.

A motive for the killing remains under investigation, police said.