Here I was, happy as can be about finally solving a minecart problem, when one of my citizens(thankfully just a fisherdwarf) was found drained of blood. I immediately started searching for the vampire, but he didn't even show up when I tried revealing him in dwarf therapist. I used DFhack to check for cursed creatures and there he was, a certain En Sinokenom. Now that name didn't ring any bells, but that was to be expected, so I looked through my dwarve's art. While I was searching I noticed that the human diplomat was visiting and a faint memory of him being a vampire law-giver surfaced. I checked, and yes, he was En Sinokenom.
I had never heard of this happening before, but looking at the justice screen there was indeed a witness who accused him of the murder. I promptly convicted him but while he now appears in the list of criminals, he also seems to have diplomatic immunity as there is no sentence pending.
So now I have the option of either killing him and inciting a war with the humans or leaving him be to come snack on my citizens once every year.
EDIT: Coincidentally the fisherdwarf was apparently out on bail having done all but 4 days of his 101 day sentence for failing to construct toy axes for the baron(one of my dwarves inherited the position for a different site). I suspect a collaboration between the nobles.