The problem is, if you're used to handling the stress of life with pot and alcohol (and many, many people are), it's almost impossible not to turn to it when you're facing the kind of life crisis that this man is. He's already proved his lack of maturity and intelligence when his actions cost lives so this is no surprise at all. I suspect that if I were dealing with the guilt from something like this I'd probably want to hide my sorrows behind a marijuana haze too.
Steve