Why Did 12-Year-Olds Stab Friend for Slender Man? Slender Man may be a relatively new meme, but it's exploded in popularity.

June 3, 2014 -- Criminal and psychological experts say they’d be surprised if investigators didn’t find evidence of psychological problems in either of the 12-year-old Wisconsin girls who allegedly tried to stab their friend to death over the weekend.

The girls told police they attacked their friend in the woods to please an internet meme called Slender Man, a fictional character who hunts children and has no face, according to the Associated Press.

The girls thought if they killed their friend, Slender Man would reveal himself, and they could prove he was real, according to the Milwaukee Journal-Sentinel.

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“Seeking this literature, the sites where these horror stories are, without having adult guidance could be very harmful even if it doesn’t turn into an act like this,” said Felipe Amunategui, associate program director of child psychology at University Hospitals Case Medical Center in Ohio.

Amunategui said he knew too little about the girls to determine anything specific about their psychological conditions, but he would be surprised if at least one of them didn’t have an issue of some kind. He said fantasy isn't unusual for 12-year-olds but this "perversion" of that is "extremely unusual."

The Slender Man meme began on a web forum called Something Awful as part of a Photoshop contest in 2009, according to the website KnowYourMeme.com, but it has since grown into a kind of internet folklore.

The tall, slender man in a suit has no face and can sprout tentacles from his back.

The story has been morphed and retold on amateur fiction-writing sites, in YouTube videos and on message boards. There are dozens of Twitter accounts claiming to be Slender Man, and the so-called official (yet unverified) Slender Man account has about 89,200 followers.

The meme was almost a movie and a videogame, but both didn’t happen because Slender Man is actually copyrighted by Eric Knudsen, who goes by the pseudonym Victor Surge, according to copyright records.

Still, Kenneth Lanning, a former FBI agent who worked in its behavioral science unit for violent crime, said the meme alone is not to blame any more than superman was to blame in the 1950s for children jumping off their roofs.

“If these girls get so enmeshed in the fantasy of Slender Man, there’s some kind of a problem," he said. "It may have lowered their inhibition, but that's not what caused this ... Hundreds or thousands of children talk about, tweet, text message about Slender Man, but ... they've never killed anybody."