Longtime documentary filmmaker Liz Garbus prefaces Lost Girls, her debut narrative feature, with a peculiar subtitle: An Unsolved American Mystery. Before viewers know a single detail about this based-on-a-true-story, they’re already aware of the fact that the ending isn’t going to be wrapped up nicely for them. Granted, that subtitle is taken from the book by Robert Kolker that the film is based on, but it’s certainly an interesting choice from a dramatic standpoint. A veteran of the true-crime genre who has worked almost exclusively with HBO for nearly 20 years, Garbus surely knows how important it is to hook the viewer from the start by withholding key information. When the outcome of practically any given case is just an Internet search away, sprinkling tantalizing bits and pieces through a story — whether documentary or drama — is essential to sustain interest in a modern true-crime yarn. This can be seen in contemporary pillars of the genre such as This American Life offshoot Serial or Netflix’s Making a Murderer, both of which utilized this mystery-box approach to great effect. The outright rejection of the genre’s standard format must serve a purpose, though. After all, Garbus certainly understands what she’s doing ... right?

It’s 2010 in Ellenville, N.Y., a village just south of the Catskills that sits halfway between Albany and New York City. A helpless woman screams in terror as a pair of headlights chase her down a dark road. A twinkling rendition of Stephen Foster’s “Beautiful Dreamer” drowns out her cries. After the bemusing subtitle, this first scene is more akin to the kind of beginning that viewers have come to expect from the genre. Although the audience members know nothing of the story so far (apart from the absence of a resolution), they can be sure they’ve just witnessed the murder that will serve as the driving force of Lost Girls. The film then flashes back to earlier that morning and introduces construction worker Mari Gilbert (Amy Ryan). Her audacity to call out her boss for cutting her hours tells us she’s both foolhardy and hard-working. Her fiery response to the news of her daughter Sarra’s (Oona Laurence) suspension — learned as she heads to her second job at a local diner — illustrates that her impetuousness isn’t just reserved for the job. It follows her home, too, which is perhaps why her oldest child, Shannan (Sarah Wisser), left for Long Island as soon as she was able.

There’s no real bad blood between mother and daughter, however. In fact, Shannan is supposed to be joining her mom and sisters Sarra and Sherre (Thomasin McKenzie) for dinner that night. Still, the relationship is rocky enough that Mari doesn’t think much of it when Shannan never shows. It takes her boyfriend (Brian Adam DeJesus) and a strange doctor (Reed Birney) calling the house for the worry to really set in. Naturally, the same blend of diligence and impulsiveness that drives an average day in Mari’s life ends up fueling the family’s search for Shannan. Their exhaustive investigation quickly catches the attention of the local police and soon tips them off to a conspiracy much larger than any of them could have anticipated. A killer on Long Island is preying on sex workers and somehow covering their tracks well enough to leave law enforcement completely perplexed. Despite obviously being a true-crime mystery from the start, this is the point where Garbus’ interest in Lost Girls becomes clear. The filmmaker has been drawn to horrible crimes riddled with thorny details and complex women for most of her career, and this fictionalized account of a real story is rooted in the same pet themes found in many of her documentaries.

Getting the police to prioritize the killings and the disappearance of Shannan is like pulling teeth for Mari. As the plot thickens, the film’s subtitle feels less like a subversive undercutting of the dramatic tension and more like a running indictment of the police. Every time the investigators (Gabriel Byrne and Dean Winters) spearheading the case stumble into a roadblock, that word “Unsolved” stings a little bit more. (It’s worth noting that, similar to the Zodiac Killer, the Long Island killer remains at large despite killing 10 to 16 women over the span of 20 years.) This is a go-to criticism for Garbus. Her previous project for HBO, Who Killed Garret Phillips? (2019), is a three-hour evisceration of law enforcement in Potsdam, N.Y. Her debut doc, The Farm: Angola, USA, follows life in a maximum-security prison and explores the failings of the criminal-justice system. Garbus’ fixation on the specific weaknesses of American justice makes Lost Girls an ideal debut for her, but the script by Michael Werwie— who also wrote the subpar Ted Bundy biopic Extremely Wicked, Shockingly Evil and Vile (2019) — simply isn’t the right match for someone of her stature within the genre. It’s an awkward fit: a two-time Oscar-nominated director and a writer who specializes in Netflix Original true-crime dramas.

There’s no reason that this compelling and horrific puzzle should have been sentenced to Lifetime-movie lows when it could have gotten the Zodiac (2007) treatment. Above all else, Werwie’s hasty pacing and stale dialogue completely suck the life out of Lost Girls. Amy Ryan and Gabriel Byrne are genuine talents, and Thomasin McKenzie is certainly a promising up-and-comer, but not even their collective aptitude is enough to right the wrongs of this script. Bogged down by genre trappings from the very start, Garbus would have been much better off adapting this material into a gripping and thorough documentary. It could have been on par with some of her best work, but, frustratingly, viewers are left with a warmed-over narrative feature instead.

The particulars of both the search for the Long Island killer and the lives of the Gilbert family deserve a better feature than Lost Girls. Although Garbus does her best to transfer her talents from one method of visual storytelling to another, she’s held back by a meager script that gradually loses focus on its target after spending so much time hovering right over the bullseye. As Mari’s fight for the attention of her local PD grows more desperate, the film struggles to maintain a similar grasp on the viewer. Somehow, even though it’s based on one of the most fascinating murder mysteries of the 2010s, Lost Girls manages to take the unanswered disappearance of Shannan Gilbert and the unsolved case of the Long Island killer and render them tedious. Garbus and Werwie’s efforts still feel disappointingly futile, failing to shine a bright enough light on a series of tragic deaths. Perhaps An Unremarkable Netflix Original would be a more accurate subtitle.

Rating: C

Lost Girls is now available to stream from Netflix.