In a previous question, I brought up the concept of sanctuary towns, towns populated entirely by people who know about the population of immortal (as in they can't get old or sick; they can still be killed) supernatural creatures living in secret amongst humanity. Everyone in the town is either an immortal or a human who knows that immortals exist, and they make sure to keep non-immortals from visiting by means that this site so awesomely helped me work out. This allows the immortals in this town to openly be themselves without having to worry about things like having to pass for human and the like.
Now, immortals generally live as members of various clans, which each have territory as well as vague borders with the territory of other clans. Said clans... do not always get along, and frequently get into skirmishes or try to drive rival clan members out or kill them to expand their territory. But when I've tried to visualize how these turf wars play out, one part of it is giving me serious trouble. When it comes to most places where immortals live, where there are no sanctuary towns and it's just a question of killing or ousting the minority of the town or city's population that belongs to rival clans, that I think I've got the hang of the details of. The problem comes with these sanctuary towns.
Killing all of the rival vampires or werewolves in a normal city or even a normal state would probably fall sufficiently within normal expected death and crime rates that they could proceed with business as usual as long as the murders weren't traced back to them. But you can't do that with a sanctuary town. If you try to take over a sanctuary town like it's some kind of military siege, killing or even just driving out all of the rival clan's inhabitants... I just don't see how you could possibly keep people from finding out that the inhabitants of that town have completely changed overnight. These towns may be secretive and generally isolated, but I seriously doubt that'd be enough that the entire population could be replaced overnight and nobody would ever notice. These towns have enough trouble dealing with the inevitable interactions they have to have with the state government without having to deal with the issue of most of the population changing completely since the last time they checked. So it seems obvious that these clans are going to need some slightly different tactics if they're going to keep safety in numbers from making their rival clans' strongholds completely unassailable.
If an immortal clan really wanted to expand their territory and completely take over one of their rivals' sanctuary towns, how would they do this without getting the unaware humans of the outside world extremely suspicious about the massive death toll or exodus that would be sure to follow if they actually succeeded?