This question is of course entirely hypothetical, but I am curious as to what crimes would be applicable in this situation. Alternatively, you could interpret the question as: If someone pretending to be a vampire broke into someone's home, drained at least one person's blood nonconsensually, and escaped undetected, what could the perpetrator's charges be if caught?
For clarity's sake, I can mention that this particular question came about in reference to the villains from the videogame Gabriel Knight 3, who are nominally vampires but turn out to be pretty different from the 'traditional' definition and so lack pretty much any of the mythical weaknesses or restrictions associated to them (they also lack any kind of communicable 'vampiric condition', but are merely humans who have greatly extended their lifespans by stealing and drinking magical blood).
One additional detail it didn't occur to me to mention earlier is that to escape detection, they use magic to put everyone in the vicinity into a deep sleep, which in a more realistic frame I suppose could be equated to something like nonconsensual administration of hypnotic psychoactive drugs. Based on what's been said I'd think something like that would also fall under assault, but I'm not sure.