Immortal characters in the modern day: what can legally happen to them?

[TheStranger]

The ability to manage publicity is kind of the wild card here. A man claiming to be immortal could become a celebrity, or he could be dismissed as a lunatic (or both). He can probably go public at any time, and the government can't stop him, unless it bypasses the normal transparent court system completely (which isn't impossible, even "legally"). But he needs some kind of proof, and there's just no guarantee how anybody will respond to that sort of thing. Unless and until he knows for sure that his cover's already blown, he won't want to play that card. And unless he's taken the time to set up his proof in advance (which in itself risks discovery), claiming to be immortal won't do him much good. I mean, imagine that you were on a jury and the defendant raised that as his defense - I can't think it would go well.

This assumes that the immortal has slipped up, but his secret isn't widely known. Now, if you have an immortal who has already gone public and convinced the world, you have a different situation. People will be watching, so it's much harder to just make him disappear. You can probably convict him of something (tax evasion is indeed a classic), but putting him in prison for a couple years doesn't accomplish any major goals, because it's still fairly open and people will keep an eye on him - you need him to disappear from the system completely so you can get him into your secret lab and run some tests. And prosecuting could raise his profile even further if the government plays it wrong.

In that case, the best solution might be to throw a pile of money at him in exchange for his cooperation in some minimally-invasive testing and a promise to stay quiet about it.