They ran after police said someone put on a clown hat and a joker mask inside one of the Century Boulder theaters.
The incident immediately recalls fear brought on by the Aurora Theater Shooting.
Boulder Police arrested a 17-year-old male who told them he knew about the Aurora shooting - but wore the mask to scare his friends.
He also told police he wanted to dress as the joker next Halloween.
The teen is being charged with five counts of menacing - because those who ran from the theater feared their safety.
His name isn't being released because he is a minor.
(KUSA-TV © 2012 Multimedia Holdings Corporation)