A relative stopped a planned school shooting near Plainfield on Friday after pinning down a boy who police said was on his way to Grand Prairie Elementary School with a gun. Deputies later detained the student at a home on the 2400 block of Helmar Lane in unincorporated Plainfield Township, where they say they found a Glock handgun, a backpack packed with multiple loaded magazines, knives, an accelerant, gloves and other items.

Police were called a little before 1 p.m. on the last day of classes for Plainfield Community Consolidated School District 202 to the home for a suicidal male subject. When deputies arrived, they found the boy and a relative inside. The relative had dialed 911 and was holding the boy down, investigators said, as the situation escalated from a mental-health call into a potential mass-casualty scare. The boy was later taken to a hospital to be evaluated, and police said he made both self-harm statements and homicidal statements to paramedics at the scene.

The boy was identified by the district superintendent as a freshman at Plainfield Central High School, and police said he had a documented history of poor attendance. That detail does not explain what happened Friday, but it places the case inside a school system that was already ending classes for the day when the threat emerged. There was no active threat to students or staff, Glenn Wood said, even as the district moved quickly to put extra police at every facility for the rest of the day.

Staff who were still in school buildings after the arrest were placed on lockdown, and outdoor activities were moved inside. The response showed how fast a local emergency can spread through a community when a shooting is believed to be imminent, even before anyone is hurt. Similar moments have rattled other public places before, from a shooting scare outside the White House to violence outside a courthouse and a deadly shooting in Fort Worth, but this case ended before the boy could reach the elementary school.

The Will County Sheriff’s Office is investigating the incident, which leaves one central question answered and one still hanging over Plainfield: the attack was stopped, but what led a freshman to leave home armed and headed toward a school on the last day of classes?