Let's say you're a pig farmer and you hire a sex trade worker.

While she's in your company, your dark side erupts and you kill her.

That is murder, as I understand the law, and would probably qualify as second-degree murder.

But then you go out and commit five more such murders. You get rid of the bodies by butchering your victims and feeding their remains to your pigs.

At what point does your pattern of behaviour start to become planning and deliberation, thus making you guilty of first-degree murder?