I think Leo aswell, he was in the episode alot which is unusual, he oculd of been phoning Calvin for his help after regretting it or something lol.
I dont think it was Louise, too drunk, she was sick from drinking not cos of what she did.
Obviouslty not Katy or Justin,
Not Warren - infact i think the he ran over Justin lol! that would of been a twist
Max i dont think so, he was too depressed
OB possibly. OB or Leo