He was pretty young for it to have been natural causes, and accident would have been announced -- at least that's my guess. All we can do is speculate, and even to me speculation feels a little ghoulish. Nevertheless, the indicators are there to make it seem plausible.
Maybe it was the result of a clinical condition. That seems more probable than any Shakespearean plot twist wherein his conscience caught up with him.
Does that seem harsh? Don't care. I may not wish the guy genuine ill, but neither am I going to be some poseur who pretends, after the fact, that "he wasn't that bad." He was that bad. He was a total fucking shitball of a human being. I'd still have rather have seen him have an Ebenezer-Scrooge-After-The-Third-Ghost epiphany than off himself, but I'm not going to be dishonest about who he was, nor do I think he'd want any of us to do so.
He was a cunt. Now he isn't one anymore. I hope he has embraced the peace in death that he never seemed to want in life.