It is a situation that 2 boys were going to fight.
A: いくぜ やろう！
B: こいっ ぶっころしたるっ
I know that て- form verb followed by したる or してある indicating a completed action in preparation of something. In this case, they were going to fight so there was no one killed. I would like to know why this form was used instead of しておく. Probably, I misunderstood the concept.