Anthony Horowitz said this quote
“ I had chosen to play the detective—and if there is one thing that unites all the detectives I've ever read about, it's their inherent loneliness. The suspects know each other. They may well be family or friends. But the detective is always the outsider. He asks the necessary questions but he doesn't actually form a relationship with anyone. He doesn't trust them, and they in turn are afraid of him. It's a relationship based entirely on deception and it's one that, ultimately, goes nowhere. Once the killer has been identified, the detective leaves and is never seen again. In fact, everyone is glad to see the back of him. ”