KENOSHA, Wis. — A 13-year-old boy is being investigated after walking to his former elementary school in Kenosha, Wis., with a black bag and backpack that appears to have been a threat.

This is one situation where cops say stopgaps worked. Authorities said they were able to prevent a possible shooting that could have happened inside the elementary school.

Police said the teenage suspect tried to enter through several doors and was eventually mistaken for a student and entered.

Neighbors near Roosevelt Elementary said they heard sirens screaming down the block Thursday morning.

“All of a sudden, a SWAT truck pulled up,” said Jabbar, who witnessed the arrest.

By then, parents had already gathered outside, desperate to reach their children inside.

Police said inside they stopped a 13-year-old former student with a backpack and a black bag. He has yet to be charged with any crime and is a minor, so his face has been blurred.

Investigators also discovered a video they said showed the boy holding a gun, though they did not say when it was filmed.

“This video should not have been seen by us today. This should have been reported to us sooner,” said Kenosha Police Chief Patrick Patton.

Police said his online history is also alarming. By mid-afternoon, police had found a suspect they said shouldn’t have gotten so close to the young children.

“We know there were Internet searches and all the red flags that we would look for and expect someone to report were there,” Patton said. “We narrowly missed a tragedy today.”

Police said those Internet searches the suspect did were related to school shootings. They also say the teenager had been sharing threatening videos and comments for weeks before today’s incident.