cut scene
Five wizards in gather at a monolith in long forgotten ruins floating in the Astral Sea. Discerning eyes can see the silver tether each has back to their body on the Prime Material Plane.
Diviner: My magics have discerned a new threat to us. A band of adventurers have set their eyes upon us, hoping to kill us, one by one.
Courtesan: A new game then? This may be entertaining for a short while.
Bladesinger: So, Cat and Mouse again?
Diviner: No, these adventurers pose a legitimate threat.
Bladesinger: Ah, so Cat and Cat.
Diviner: I have been researching them. My scribes have copied manuscripts on each of them, including their names, likenesses, strengths, and weaknesses.
Courtesan: Found any leverage on them yet?
Diviner: They're not saints. But so far, the most serious crimes I've found are grand theft.
Courtesan: Good enough to set the law on them, and the bounty hunters.
Bladesinger: I'll speak with the Elven Courts too, have the Rangers hunting for them.
Enchanter: Let's do to them, as they attempt to do to us: divide and concur. I'll set upon their most vulnerable my succubus, and see if I can peel a member of their cabal away, and get him involved in crimes of a more serious fashion.
Articificer: I'll start working up plans for a direct assault on them. Get them running from the law, bounty hunters, and rangers. You ahead and try to peel off a member. I'll set the trap in a place they're known, where they think they're safe. Make it look like their one safe harbor. But with our armies combined, we can turn the whole place into a killing field. Give me time to read through this tome of intelligence you've already gathered, and I'll find our kill zone...
EDIT: In a feudal society, the lord of any given land, owns anything on or in that land, unless there is specific documentation or precedent saying otherwise. So, those ancient ruins over there? Typically, it would be the property of the local lord. He owns it. He owns anything found there. You take anything out of those ruins without the permission of the owner, and that's theft. If the value is sufficiently high, it's grand theft. The local lord need only push his right. It's easy to get them to do so, when court wizard whispers sweet words in your ear that it would be beneficial to you both if you were to claim your rights. Theft or grand theft is the easiest crime to accuse your PCs of, since PCs are a bunch of looters.
Technically, bounty hunters go after people who have jumped bail. But people like them can be hired to go capture and return people so they can stand trial. Normally this was done by officers of the court, though they may get the help from the local sheriff or lord. But once you cross out of the nation's borders, you'd normally have to ask the nation they're residing in to arrest and extradite them for you. This often wouldn't happen, especially for lesser crimes. But you could hire people to cross over into another nation, and go bring the person back to stand trial. It would technically be kidnapping until you crossed back into friendly territory, but such things were (and sometimes still are) done.
Once someone's crossed over into more serious crimes, such as murder, extradition becomes easier. People usually don't want a pack of roving murderers wandering their lands. And once you start hounding (perhaps literally) someone with bounty hunters, it's almost inevitable that they'll eventually surrender (which PCs never do) or murder.
