The Gun!!!
I have just seen 15 min of the first episode, and I think that the details in series like this is very important! The guy at the arcade place was killed from a gun and the killer was standing near him! I assume that the killer was a vampire and thats why you couldn't see him, but why could you not see the gun or the clothes for that matter? The clothes are actually something that often is invisible in vampire movies (in mirrors)!