SymphonicFire

They wanted to catch a suspect that was threatening a member on staff. They had to have a lock down to check everyone's phone in that grade. 

Okay. But why did they make you sit your butt on a floor of a dark room? seems like an odd thing to do if all they want is to check your phone. x3

They wanted to trap the suspect in the classroom without alerting them. Everyone thought it was a drill...except for the few who noticed the principal say "Teachers please check your emails" at the end of the announcement.