'Beware the Slenderman' Review: HBO's documentary is a chilling internet case study

You have probably already heard of the Slenderman, an incredibly tall, faceless entity in a black suit that usually resides in the forest. Does he also stalk children? Is he a murderer? Is he a twisted guardian angel for said children who feel reclusive, alienated and bullied? Could he be cute in a Jack Skellington, Nightmare Before Christmas kind of way? 

The Slenderman can assume all these characteristics and more, the result of a fictitious character spawning from the internet, its influence spreading like wildfire thanks to short stories, video games and some chillingly realistic YouTube videos. But the most disturbing branch in the Slenderman lore? He allegedly told two kids to murder their best friend. 

That's what two 12-year-old girls in Waukesha, Wisconsin — the subject of HBO's chilling true crime documentary, Beware the Slenderman — thoroughly convinced themselves. The documentary, which explains Slenderman's origins and tells the story of Anissa Weier and Morgan Geyser, is a harrowing case study of the internet's impressionable influence on children. 

Though Beware the Slenderman ultimately feels incomplete, it's effective in portraying how a perfect storm of the internet, mental illness and social isolation can make a seemingly innocuous obsession go too far. 

There's no clear-cut villain in the disturbing case 

When Beware the Slenderman premiered at SXSW in March 2016, director Irene Taylor Brodsky was quick to caution that the blame for what happened in the small Wisconsin town — when two girls attempted to murder their best friend to appease the fictional boogeyman, stabbing her 19 times — can't be pinned to one single thing. It might be easy point fingers at either the internet or the girls, but it's really a combination of both. 

On one hand, the influence and spread of Slenderman online can't be discredited. He first appeared as part of a Photoshop contest in 2009 and rapidly circulated. This was largely due to unsettling fan fiction on the horror site Creepypasta, though the lore of Slenderman eventually branched out to popular video games like Slender: The Eight Pages. For what it's worth, the character is now being developed as a horror film by Screen Gems. 

In the words of a teen from a YouTube video featured in HBO's documentary: "If you don't know who Slenderman is, you're living under a rock." 

For the girls, Morgan and Anissa, Slenderman — who, they claim, asked them to kill their friend so he wouldn't harm their families — was convincingly real for different reasons. As the documentary unveils, Morgan, now 15, is diagnosed with early childhood schizophrenia, from which her father also suffers. Anissa, now 14, was a bullied outcast at school whose social circle began and ended with Morgan. Without other peers to interact with, coupled with Morgan's potential delusions, the pair was particularly susceptible to the Slenderman myth. 

Meanwhile, Morgan and Anissa's parents are left to wonder what they could've done differently to help their children — and once again, there's no definitive answer. Anissa's dad says there was an open-door policy in the Weier household, where internet usage was monitored and limited in favor of family time. While Morgan's father suffers from schizophrenia, the Geysers didn't see any glaring signs in her behavior to indicate she had the same disorder. The parents seem sincere, soft-spoken and shell-shocked in the documentary, which makes their children's predicament all the more upsetting to watch. 

Morgan Geyser appears in court.HBO

Beware the Slenderman was released too soon 

If Beware the Slenderman is HBO's answer to Making a Murderer, it similarly would've benefitted from being turned into a miniseries — there's a lot to unpack with both the girls and the Slenderman myth — or having its release delayed. Unfortunately, Beware the Slenderman feels incomplete because the legal process behind the girls' case is ongoing. 

The meat of the legal narrative is whether the girls would be tried as adults — and to be clear, that is important context — but the documentary ends without the outcome of the trial itself, which should happen sometime this year. It would be the equivalent of Making a Murderer detailing the evidence to support Steven Avery's innocence without ultimately showing the verdict in his trial.  

Oddly, the biggest resolution the documentary provides is equal parts unsettling and mythical. While Morgan and Anissa committed the disturbing act to appease the fictitious Slenderman — in their own words, to become his loyal proxies and retreat to his mansion in Nicolet National Forest — the girls themselves have now become part of the Slenderman mythos. 

The documentary concludes with a compilation of internet fan art depicting the girls alongside Slenderman, their likeness a permanent relic of the disturbing virtual rabbit hole to which they were obsessively drawn. That's creepier than any fable about the internet's boogeyman. 

Beware the Slenderman premieres on HBO at 10 p.m. Eastern Monday, Jan. 23.