"Because" is a bit of a red herring. I'd bet there's been dozens "after" smoking a joint!
You would loose. Except possibly if someone was dumb enough to try and guard the fridge after a joint or three.
IF there are any murders related to pot it is strictly because it has been deemed illegal. Anything that people want that is illegal brings in the criminal element.Like the government. Definitely a criminal organization complete with an enforcement arm.