Airs Monday January 23 10:00 PM on HBO

“Fear the man, the Slenderman. For he can do what no one can.”

2014: Two 12-year-old girls lured a classmate into the woods — where most bad things happen in stories like this — and stabbed her 19 times. It was shocking in its own right, but equally surprising was the reasoning the two pre-teens had for their attempted murder: they wanted to impress a fictional boogeyman. Known as The Slenderman, this tall, faceless creature stalks the woods with tentacle-like arms. It flocks to outsiders, particularly children, and can either be a guardian angel or something far, far worse — depending on who is telling the story.

The young stabbing victim lived, and the two girls responsible for the deed were caught and imprisoned, kicking off lengthy litigation involving just how to treat the assailants — as mentally underdeveloped children, or as cold-blooded adults. This is the focal point of Irene Taylor Brodsky’s interesting, but unfortunately muddled documentary Beware the Slenderman.

Unlike other mythical monsters like vampires and werewolves, the origin of Slenderman can be easily traced and pinpointed: Eric Knudsen created the character on the Something Awful message boards in 2009 as part of photoshop contest. The goal was to create a realistic portrayal of something paranormal, and while most participants took to uploading photos only, Knudsen thought to add a caption to the images he created, the most prominent of which showed a flock of disturbed looking children caught mid-march towards their photographer while an impossibly tall, blurry figure trails behind them. “We didn’t want to go,” the caption on this photo read, “we didn’t want to kill them, but its persistent silence and outstretched arms horrified and comforted us at the same time…” Creepy stuff, sure, but also clearly fictional. And yet, Knudsen’s creation, dubbed Slenderman, took on a life of its own. It became the star of a series of short, scary internet stories known as “creepypasta” before branching off into YouTube videos and computer games. And, curiously enough, some impressionable purveyors of the character began to believe he was real.

That’s where 12-year-olds Morgan Geyser and Anissa Weier come in. The two friends took their fandom of Slenderman to the extreme when they decided to kill their friend Payton “Bella” Leutner as an offering to the character. Geyser and Weier believed, apparently, that killing Leutner would enable them to live with Slenderman in his mythical “Slender Mansion” somewhere deep in the woods. It would also appease the monster, and keep him from killing them and their loved ones. Brodsky’s film goes into the chilling details of the crime, and attempts to deconstruct the Slenderman legend and explain how it passed from simple meme-dom into something akin to folklore. It all sounds very compelling, but Brodsky’s execution leaves much to be desired.

The filmmaker peppers Beware the Slenderman with interviews from experts — including Richard Dawkins, of all people — weighing in on both Slenderman and the nature of memes in general. But for some bizarre reason, these talking-head interviews are conducted via Skype, and noticeably so. Each subject sits gazing into his or her own laptop, usually wearing earbuds, while choppy video plays back their comments. Perhaps Brodsky is using this element to reflect on the internet-based origins of Slenderman, but if so it never comes across that way. Instead it’s a distraction. At one point an interviewee stops talking mid-sentence to yell out to someone off camera that she’s conducting an interview via Skype. This is the type of detail that could’ve easily been left on the digital cutting room floor.

When Beware the Slenderman chooses to focus on the so-called “Slender Man Stabbing”, it can often be effective and downright disturbing. Police interviews with the two girls post-crime are bound to give audiences the creeps: Weier seems nervous and remorseful of the crime, but also completely detached from reality, while Geyser — who was later ruled incompetent to stand trial — comes across as completely unrepentant and even a little annoyed at the entire situation, as if police are wasting her time by questioning her.

But Beware the Slenderman can’t seem to get a grip on what it wants to be. At times, the narrative completely breaks down so that Brodsky can string a series of YouTube clips together with no real rhyme or reason. Just when the film feels as if it hass found its groove, it changes course to focus on the traumatized family members of Weier or Geyser, only to then awkwardly cut back to a lengthy discussion on memes. There’s no rhyme or reason here, and the film suffers as a result. We walk away feeling muddled, unsure of just what Beware the Slenderman is trying to tell us. There’s no doubt a message here, but it gets lost in all the static. If a quick trip to Wikipedia to read up on the stabbing events and on Slenderman himself yields more insight than your documentary, you’re doing something wrong.