Answer: The Cook
Most people think that the first one to die is Mr. Body, but at first the movie makes you believe he is and then they find the cook. But in the accusations they show that Mr. Body faked his death and was shown getting up to follow the rest of the group, but the killer crept up behind him and killed him, then put him in the bathroom, therefore the first one to actually die is the cook. Confusing huh?