I have a terrible one, one that affects me personally.
My junior year, (1999-2000), some of my friends, two males and one female, killed the female's father. It was a brutal murder.
About three weeks later, the police had the idea that all three of them were at the high school (which was funny since one of them graduated, one of them was a drop-out, and the other one had been skipping school for over a week).
When the lockdown happened, I was in the Home Ec room, during lunch, about to have an FBLA meeting. Altogether, there was about two other guys and about a dozen girls. One of the Home Ec teachers rushed in, freaking out, and calling in some of the students (all female) for their protection.
We stayed in there for about 2 hours. During this time, I stayed at the front door as a "watchman," which the teacher didn't like very much. Also, me and the two guys decided that, if someone was running around the school with guns aiming to kill us all, we'd go out fighting. We grabbed the sharpest knifes we could, ready to kill the "gunman" that we had conjured up.
About half an hour later, our security guard and a Washougal police officer came in & told us it was okay.
The people they were looking for were on the other side of the city at the time of the lockdown. We really had no reason to freak out.