I need a "Bounty Hunter" side quest.

[jovial stream]

So my three players are in a city, gathering intelligence on a local artificer who's luring people into cursed bargains with a devil. This city is run by a clan of Dwarves, and the artificer is a citizen in good standing, so the players are going to need to gather ironclad evidence of his nefarious activity to see him stopped and/or brought to justice.

One of my players is a "Bounty Hunter" who has a vampire-like affliction that requires him to periodically feed on humanoids, and he tries to sate this need by taking "dead or alive" bounties and always choosing the "dead" option.

Anyway, my players have already announced their intention to go visit the Boss Dwarf at the top of the next session and see about finding a bounty they can legitimately investigate while secretly investigating the evil artificer. But I don't have any idea who the dwarves who run this town would want dead. It's a relatively small city, with a large number of dwarven guards keeping order. If the dwarves know of an individual criminal in need of lethal justice, they have enough manpower to find that person, or at least run them out of town, relatively quickly. I want to honor my player's desire to have a manhunt, but I can't figure out how to work one in.

[dire island]

Even a small city would be big enough for criminals to hide.
Its pretty much impossible for them to have complete surveillance unless its some sort of totalitarian police state.

However, maybe the criminal in question is a wizard, so they have spells and items that make it a lot easier to escape notice.

[jovial stream]

The Dwarves in this town have lots of weird cultural taboos, so maybe the Bad Guy is somehow exploiting that by surrounding themselves with something the dwarves find extremely distasteful or blasphemous....

It's not quite a totalitarian state, but the Dwarves definitely have full control. I actually designed it this way on purpose, to make it VERY CLEAR to my players that they have to BEHAVE themselves in this town, and not solve all their problems with violence. They could easily just solve their current problem by murdering the artificer, but they can't do that, because then an army of Dwarves would be upon them. It's worked perfectly to make their current mission feel like a covert investigation instead of a hack-and-slash dungeon crawl, but it hasn't left any room for there to be known bad guys at large.

[carmine schooner]

People who come in from the outside who aren't in the state sphere of influence.

They enjoy some level of protection of course due to often being affeliated with foreign powers. So simply arresting them leads to a headache. Much easier to have them be bounty hunted for some crime dug up outside of the city or one they happen to commit while intown.

The city government isn't the one officially posting those bounties. They're "private citizens"

who may or may not be bankrolled by city coffers if it's in the interest of the ruling powers

Doing the arresting or assasination via means of private citizen bankroll gives the city some manner of deniability as getting arrested or dying is happening due to a private citizen posting the bounty rather than the government taking an actual stance

That's one idea at least.
It feels a little wonky to me but maybe the wonky dysfunctionality of it can be part of the flavour