Samantha Dionysus is the god of wine, and having a bacchanal led them to the first murder. Remember who influenced this group is by ancient Greek culture.
This answer contains spoilers… (view spoiler)[All of the drug and alcohol usage, especially towards the end of the book, made me question the trustworthiness of Richard and the other characters. There were many odd happenings throughout the book that seemingly existed to create a state of paranoia - the copious amounts of alcohol and drugs elevated that feeling for me. (hide spoiler)]