If i was a serial killer i would be David Berkowitz.
Originally believed to be a paranoid schizophrenic, David Berkowitz (the Son of Sam), claimed to be plagued by demons that came in the form of dogs, when the dogs would howl, that was their signal for him to kill. He said that the dogs would call out to him for blood and death, and their cry's would only stop by killing and assaulting over 6 New York women.
In a later interview Berkowitz revealed that the demon story was a conscious fabrication that he had made up to force the police into believing he was insane if he was caught. He also confessed that he would become sexually aroused when stalking his victims and would sometimes come back to the crime scenes and masturbate while envisioning his prior killings.