This is a situation in which police say the stopgaps worked. Authorities said they were able to thwart a possible shooting that could have happened inside the elementary school.
Police said the teenage suspect tried to get in through multiple doors, and was ultimately mistaken for a student and buzzed in.
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, witness to the arrest.
By then parents had already gathered outside, desperate to get to their children inside.
Police said inside they'd stopped a 13-year-old former student with a backpack and a black duffel bag. He has not yet been charged with a crime and is a juvenile, so ABC7 has blurred his face.
Investigators also uncovered video they said shows the boy holding a gun, though they did not say when the video was taken.
"This video shouldn't have been seen by us today. This should have been reported to us earlier," said Kenosha Police Chief Patrick Patton.
Police said his online history is also alarming. By mid-afternoon, police had found a suspect they said never should have made it so close to young children.
"We know there was 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 allegedly did were on school shootings. They also say the teen shared threatening videos and comments for weeks leading up to today's incident.