You just broke out of a maximum security prison and are on the run. You are an inmate on death row with your execution date coming up soon and all your appeals have failed, so you've got nothing to lose, and you sure as hell aren't going back to that shithole prison to die like a bitch. You managed to steal a handgun and a couple magazines from the cop you killed during your escape, so at least you're armed and have options.
You make it into town after spending a couple hours trekking through a heavily-wooded region separating the prison and this small community.
After walking down the street, you find yourself standing in front of an elementary school.
Knowing you probably don't have much time left before being apprehended, you decide to go out with a bang.
You rush into the unsuspecting school.