Why did Colorado school shooter do it?

... covered in blood, running down the stairs yelling, "Help me, help me, there's a shooter." Leytoldt said she was in yoga class and that her teacher told all the students to get into a closet to protect them. "We were having fun and laughing and then, ...

http://www.wtae.com/news/national/Why-did-Colorado-school-shooter-do-it/-/9681152/23485124/-/141c1cqz/-/index.html