If a minor drinks at a party and gets her self killed after the party. Whose fault is it?

In the court case chris archer v state of new columbia a girl named milan who is 18 drinks alcohol at a co ed fraternity party. Chris is the president of it who is having the party. She was then told to do a test as a pledge which was go raise the flag on the door. She ran up to the clock tower and fell. Chris is charged with 1st degree murder. I am defending chris archer. For anyone who knows this case how can i prove he is innocent?