Richard and Justin, the high school killers in "Murder by Numbers," may not have heard of Leopold and Loeb, or seen Hitchcock's "Rope," or studied any of the other fictional versions ("Compulsion," "Swoon") of the infamous murder pact between two brainy and amoral young men. But they're channeling it. "Murder by Numbers" crosses Leopold/Loeb with a police procedural and adds an interesting touch: Instead of toying with the audience, it toys with the characters. We have information they desperately desire, and we watch them dueling in misdirection.