やがる verb suffix (te form or masu stem) to indicate hatred and contempt, or disdain for another's action http://jisho.org/words?jap=yagaru&eng=&dict=edict

The verb of "~しやがった" is a sort of Japanese slug. It's abuseful meaning and it's often the case that a person who tend to use the word get a violent impression from usual people in Japan. And that's also used to express the feeling of a frustration by doing something bad.