Bloodborne

Murders occur, leaving a string of pristine remains for the police. They have no visible injuries except for two curious incisions on the neck. It appears the victims were attacked by a vampire. The bodies are left without blood, the lack of which is what killed them; another fact that points to a vampire. Baffled police wonder if they need wooden stakes instead of guns for their investigation.
And so begins the bizarre case of bloodless corpses for detectives Dobbs and Degree. They also follow an intriguing trail of keys that seem to connect the public buildings where the murders take place. How does the intruder enter these buildings without disturbing them? Does he turn into a fog and seep into rooms or fly through an open window as a bat? Ridiculous conclusions to the mounting question of keys.
While the city is gripped with fear, the detectives narrow their pursuit as they unravel the puzzling clues. In the end, they find themselves at the psychopath's lair, and death is the only way out.