Two cops track down a serial killer, that’s the basic idea behind, “The Little Things,” a new thriller from “Blindside” director John Lee Hancock starring Academy Award winners Denzel Washington (“Training Day,” “Glory”), Rami Malek (“Bohemian Rhapsody”) and Jared Leto (“Dallas Buyers Club”). And given this pretty terrific cast, this meat and potatoes idea may be more than enough for most audiences.