Hmm, let's see.
In elementary school, we had a bomb threat called in. School was evacuated for 2-3 hours while bomb squad searched the area. Turns out two kids from the high school thought the threat would be a funny prank, so there was never any danger.
In middle school, some girl who was bullied a lot brought a knife and a list of people to kill. She was escorted away by the counselor before anything happened. Also, some kids set the trash can and stall walls on fire in the girls bathroom.
And, while I wasn't attending the university at the time, I was in my father's office on campus. There was a shooting near our fine arts building which was on the opposite side of campus, didn't hear the shots but my father got an email and text telling us to lock the doors as there was a shooting. Thankfully for the rest of the student body, it was a personal dispute and not some crazy guy going on a rampage. It all went rather smoothly and the shooters were caught.