12 years old got stabbed 19 times by her friends same age?

Someone really make understand how, what idea, what influences these 12 years old to stab her friends 19 times? I don’t really get it. I can understand old kids in their mid teens could possibly do such thing, bu a 12 years old?

Was this a result of watching too much violent movies, games or seeing it personally? Well the bottom line is, according to CNN news indicated that these 12 years will be trial like an adult.

http://www.cnn.com/2014/06/03/justice/wisconsin-girl-stabbed/index.html?hpt=hp_t1