I voted warn then ban, because you might as well warn first knowing it will likely be ignored and then user can be banned with good reasoning.
Most people voted nuke I see, which I find a bit aggressive and unnecessary, but not against this if clearly a near majority would want this option.
Here's the thing: he has 50 accounts and so far at least a dozen of them have been banned. So, that should be instant grounds for banning, though I admit the proof isn't as spelled out as it could be.
Regardless, he's been temp banned, likely for abuse of the trust system. Hopefully its for a long time. I know he can just keep coming back under different accounts (and he has been), but banning his main accounts has to at least slow him down a bit.