Denzel Washington, left, and Jared Leto in “The Little Things.” Nicola Goode/Warner Bros. Pictures

Set in 1990, in a time before the ubiquity of cellphones and the kind of advanced, rapid DNA profiling that would come to revolutionize criminal forensics, “The Little Things” isn’t just a retro serial-killer thriller, but a deeply noirish one, harking back to not just “Seven,” but to the delicious moral ambiguity of black-and-white films from a half-century earlier.

Originally written in 1993 for an abortive Steven Spielberg project, and only now resuscitated under the direction of writer John Lee Hancock (“The Highwaymen”), it boasts a sterling main cast – Denzel Washington, Rami Malek, Jared Leto – as well as open-endedness that is simultaneously pleasurable and a bit unsettling, in both the good and bad senses of that word.

Washington plays Joe “Deke” Deacon, a sheriff’s deputy in the boondocks north of Los Angeles, from where he was drummed out of the L.A. County Sheriff’s department five years ago, after an unspecified breakdown. The details of his past only unspool gradually, in flashback, at the same time as the circumstances of a new case Deke serendipitously becomes caught up in. That’s because the new case isn’t exactly new, at least not for Deke, who was once a considered a kind of brilliant detective-savant. He speaks to corpses, sometimes literally, and they “talk” back to him, figuratively speaking. Characters refer to him as “Kojak” and “Columbo,” less in awe than in sarcasm. (Google the names, kids, if they don’t mean anything.)

While on a routine errand to Los Angeles from his exile up north, Deke gets wind of several recent murders of young women that remind him of the case that precipitated his collapse: a triple-murder that led to an obsession that led to a heart attack and divorce. His slick, hotshot replacement, Malek’s Jim Baxter, isn’t so arrogant that he won’t accept help from Deke, who demonstrates his prowess, right off the bat, at a gruesome crime scene to which Jim invites him.

Together, Deke and Jim begin to make some headway – and connections – in a case that seems to involve, by the time the film gets rolling, at least seven victims, including a female jogger who has gone missing and is presumed dead. There are two losers brought in for questioning: a guy (Frederick Koehler) with a rap sheet – or a KSO, for “known sex offender,” in the police lingo that is sprinkled throughout the script for flavor – and Leto’s seemingly squeaky clean yet creepy prime suspect, who keeps a police scanner in his apartment and has a hobbyist’s sick fascination with murder and its methods, on the perp and the police sides.

“The Little Things” – whose title refers to the seemingly insignificant details that can break a case or drive a cop crazy – isn’t a traditional whodunit. “We got something,” Deke tells Jim. “We just don’t know what it is.”

And neither, perhaps, will you.

That equivocation is what’s unsatisfying and satisfying about the film, whose true subject isn’t ever catching the guy, but, in a sense, letting Deke – and, eventually, Jim too – off the hook for the unknown somethings that life is full of, and not just for cops working cold cases.

In that sense, there’s a single word that sums up the film. It comes courtesy of a forensic police scientist whose job, as he describes it to Deke, involving the analysis of fingerprints, bite marks, blood, etc., is to make the cops “look good” in court. It’s a word that no sleepless detective  and possibly few filmgoers, except those who revel in the sweet, murky, strong black coffee that comes with lack of closure – ever wants to hear: inconclusive.

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