Two girls, set to go on trial for attempted homicide next year, allegedly said the Slenderman made them stab their friend 19 times, almost killing her.
The pair, both 12 from Wisconsin, reportedly claimed a terrifying tall, faceless man in a black suit stalked them and threatened their families.
The case, from 2014, is set to be explored in a hotly anticipated new documentary to be aired on HBO in January.
A horror trailer was released earlier this month.
But surely the paranormal figure, 8ft tall and sometimes depicted as having tentacles protruding out of his back, cannot be real?
There are entire websites dedicated to Slenderman citing evidence the spooky figure is true.
Countless videos and pictures are posted purporting to be solid proof of the creature’s existence.
They even point out representations of the Slenderman in historic cave paintings and Egyptian hieroglyphs.
Almost all believe the work of Tudor period German artist Hans Hobein shows the creepy spectre.
His wood carving “Der Ritter” in 1540 appears to show a scary alien-like figure attacking a knight.
In a documentary posted on YouTube, Christian Craughwell, a paranormal investigator, said: “This is widely considered to be the first documented encounter.
“In this carving we see somebody battling what is clearly non-human entity.
“Since that time sightings and encounters have increased hugely.”
Slenderman has even been spotted here in the UK in Cannock Chase woods, Staffordshire.
He added: “We have countless sightings around the globe with photographic evidence to back it up.”
British author and journalist David Barnett, who has written and researched Slenderman, rubbished these claims.
He said the phenomena was actually created in 2009 in urban myth forums.
Barnett claims one user called Victor Surge, real name Eric Knudsen, photoshopped old images with what we know as the Slenderman.
Speaking to Daily Star Online, he added: “Slenderman has certainly captured the imagination.
“People like these urban myths which no one is 100% sure are true or fictional.
“They are willing to believe in weird stuff and the internet age has exacerbated that.”
So what do you believe?
VIDEO THE FULL BEWARE THE SLENDERMAN TRAILER IS HORRIFYING: