From the Grey House, Book Two, Inside the Grey House:
“Whenever a Slayer is found on the streets or in a park, the body disappears and a secret organization takes over the investigation.” She slammed her hand on the steering wheel. They were at a red light and Natalia felt each second that passed as a knife in her mind. How the hell had she missed this? “If we can get him away from her, bring him back to his apartment and kill him there, the Slayers will take care of their own and no one outside of the Slayers will know about it.”