MADISON, Wis. — A 13-year-old boy who had researched school shootings online was arrested hours after he tried to enter a Wisconsin elementary school with suspicious bags, police said.

Investigators believe the boy was armed, judging by videos of him brandishing what investigators believe was a rifle and comments he made to other students, said Patrick Patton, police chief in Kenosha, a city on Lake Michigan between Milwaukee and Chicago.

“We narrowly missed a tragedy,” Patton said at a news conference Thursday afternoon.

The teen tried to enter Roosevelt Elementary School around 9 a.m. Thursday with a backpack and a duffle bag, according to police. Staff members grew suspicious and moved to question him, but he fled.

Kenosha Unified schools were placed on lockdown for the rest of the day as police searched for the boy. They finally arrested him at his home that afternoon.

The teen attends Mahone Middle School in Kenosha and was a former Roosevelt Elementary student, police said, but they have not released his name.