Palatine High School's superintendent said police told school officials that a student was involved in a community incident unrelated to the school. The superintendent said the school was not able to share that information publicly at the time.
That student tried to enter the school well after class started Monday, but the campus security team stopped them, the superintendent said. After a school resource officer took the student into custody, Palatine police showed up.
The superintendent said police arrested the student in connection with the community incident. While police were securing the student, they found a loaded gun.
The superintendent said the school didn't go into lockdown because police had taken control of the situation. Further information about the student's arrest was not immediately available.