Investigative crime documentaries have made major waves in the past couple of years, inspiring fierce fandoms of newly minted amateur detectives. 2014 brought us the record-breaking podcast Serial, which delved into the confounding murder case of high schooler Hae Min Lee. Last spring, the HBO crime-doc mini-series The Jinx became a cultural sensation, acquainting the nation with the disturbing and sometimes surreal story of alleged murderer Robert Durst. With winter came Netflix’s Making a Murderer, an instant must-binge that dug into the life and literal trials of Steven Avery, whose murder conviction has been publicly called into question. Now comes HBO’s Beware of Slenderman, a slim two-hour doc that has three hard acts to follow.

For those not in the know, Slenderman is a bogeyman born on the internet. He is tall, draped in a bespoke suit black as the night. His limbs are long. Some say his back can sprout with tentacles that attack with lightning speed and deadly efficiency. But his most disturbing and iconic attribute is his face. Or lack thereof. Smooth, white, featureless, he is the stuff of nightmares. But, also, he is a place where the lonely of the internet have poured countless hours making fan art, stories, and videos and building a mythos that is complex and surprisingly flexible. To some, Slender is not a child-snatching monster, but a dark friend who steals children from the hell of childhood.

But Beware of Slenderman is not a documentary about this internet apparition. It’s about the murder trial that made the world outside the web know his name.

On Saturday May 31, 2014, three twelve-year-old girls in Waukesha, Wisconsin went to the local park. It was the morning after a birthday slumber party, where they’d stayed up late giggling and girl talking. But in the woods, Payton “Bella” Leutner was attacked, stabbed 19 times with a kitchen knife and left for dead. Her attackers were her friends, Morgan Geyser and Anissa Weier. When they were captured hours later, the girls told the police killing Leutner was “necessary.” They told them they did it for Slenderman.

Leutner survived. Per Wisconsin law, Geyser and Weier were charged as adults for attempted murder. And this is the focus of Beware The Slenderman. Director Irene Taylor Brodsky tries to understand how two girls, who were never deemed troublemakers, turned to murder because of a photoshopped creature from Creepypasta Wiki. Employing the girls’ video taped confessions to the police, home movies of their charmingly unremarkable childhoods, and interviews with their devastated parents, Brodsky entreats audiences to see the children behind the horrific headlines. She speaks to experts on technology, on memes, on Slenderman, on fairy tales, and on mental illness. And all of this builds to seem like a sometimes crass defense of Geyser and Weier, who knew killing their friend was murder and wrong, even if they truly believed Slenderman is real.

In the film, adults line up to give their perspective on the girls’ perspective, explaining why Slenderman seemed real to them. Taylor doesn’t pick one scapegoat but several, the power of persuasion, the danger of isolation, the absorbing communities of the internet, psychosis, iPads. It becomes a yarn wall in defense of the girls, who the filmmaker never speaks to, instead giving tender close-ups of their shackled hands and ankles as they sit in court. This omission is likely a legal constraint, because of their confinement as they await trial. However, it becomes unsettling that the film about these girls talks to everyone except them. Well, and their victim.

In the wake of the Slenderman stabbing, the public was quick to rush to judgment of Geyser’s and Weier’s parents. Surely they should have seen warning signs. They should have known something was up. But as you meet them one by one, they seem totally average and totally involved parents. They knew their daughters’ friends, knew their activities, and even limited their internet time. One mother says she thought of her daughter’s interest in Slenderman as no different from her own childhood obsession with the works of Stephen King. And that’s totally reasonable. So, Beware the Slenderman grows into a defense not just of these girls who failed to separate fact from fiction to a nearly fatal end, but also of the parents who failed to prevent it. And that is an interesting angle. But it’s not enough of one to support the two-hour run time, which feels longer because of Brodsky’s dogged approach.

To her credit, Brodsky injects a sinister style into the doc by weaving in Slenderman fan art and videos that deftly display how alluring this figure is, especially to two lonely girls. Likewise, lyrical aerial shots of Waukesha build an eerie solemnity. But the film has no drive and no feeling of a finale. It becomes rudderless in its scrambles to pity these two families, ignoring the third whose daughter was nearly killed. Brodsky works tirelessly to get the audience not to judge the Geyser and Weier families, and entreats for empathy. But when no apparent attempt was made to reach out to Leutner and her family, the doc begins to feel grossly one-sided.

Beware the Slenderman wants you to believe that this tragedy could happen to anyone. Technology is so isolating, the internet so wide and unknowable. By the time it’s revealed one of the girls has a serious mental health issue that escalated this murder plot, Brodsky is so caught up in her anti-iPad jag that the film almost sprints past this key point.

Ultimately, Beware the Slenderman will serve as a disturbing introduction to this creepy character and the murder case to those totally unfamiliar with it. But if you—like me—have been following this case of a new world bogeyman, the film will offer little new, except excuses.

Beware the Slenderman made its world premier on March 11th at SXSW. It’ll hit HBO soon.

Kristy Puchko reviews movies more times on her podcast Popcorn & Prosecco

Kristy Puchko is the film editor of Pajiba. You can follow her on Twitter.