A 13-year-old boy was stopped from entering a Wisconsin elementary school Thursday morning during a suspected mass shooting, local authorities said.

The boy, seen dressed in black and carrying a large backpack and bag, was arrested hours after fleeing the scene at Roosevelt Elementary School in Kenosha, where school staff refused to let him in, the city’s police chief said.

“This suspect actually tried several front doors and entrances before he got to where our secured entrance is,” said Dr. Jeff Weiss, superintendent of the Kenosha Unified School District, at a news conference.

– The suspect became nervous. Started fiddling more. Turned around and left,” Weiss said, citing surveillance video of the teenager’s interaction with staff as they questioned him and refused to unlock a second set of doors after deeming him “suspicious.” “Their actions were heroic and prevented the unfathomable.”

Authorities declined to comment on exactly what the boy was allegedly carrying, but said he is believed to have been carrying a firearm.

A later investigation found that the teenager, identified only as a student in the Kenosha Unified School District, allegedly shared regarding videos and comments to other students for weeks prior to the incident. The suspect also conducted several online searches about school shootings, Kenosha Police Chief Patrick Patton said.

One of the alleged videos was played at the press conference, shows the suspect handling a rifle in what appears to be a home.

“This is something that should have been told to people, about his growing intentions,” Patton said. “We know there were Internet searches. All the red flags that we would look for and expect someone to report were there. We narrowly missed a tragedy today.”

The police chief encouraged parents to talk to their children about their responsibility to report anything that might happen to a parent, teacher or the police.

“Help us. Have these conversations with your children. These videos should not have been seen by us today. This should have been reported to us earlier,” he said.

No additional information was released about the suspect, and authorities declined to comment to a reporter about the boy’s custodian.