...and I actually don't think there's anything mysterious about Stephen.
Here's my hypothesis- There is a vampire faction. They may or may not be hostile. They have some sort of victory condition.
That's really it. The only reason I'm seizing on them as a threat now is because Stephen had a Night Kill, anti-undead soap is being sold, and I was DRAINED by someone last night.
I was suspicious of the vampires for different reasons Day One, namely, if I'm confronted with a group of random people, am told a couple of them might be evil, and then learn a couple of them are vampires, that's enough for me to be suspicious. They're not auto-evil, but they're the best lead I had (and have).
As for why Stephen was Night Killed... I'm not really sure. My guess is that they weren't sure he'd be modkilled (Isaac had talked about bringing in a replacement, right?), but they were pretty confident he wouldn't be protected? If this was a straight-up "normal" Mafia game, then pretty much any kill is good for the scum.
So yeah. If you think my explanations over the last few posts have been reaching, it's because your OBJECTIONS have been reaching. My central thesis is, and has been, "We have no other leads and the vampire looks suspicious."