Two 12-year-old girls are accused of plotting their friend's murder and attempting to kill her by stabbing her 19 times in a local park. Courtesy: Fox6.

TWO 12-year-old girls who stabbed their friend 19 times during a game of hide and seek apparently wanted to prove that a mysterious horror figure called Slenderman was real.

The Wisconsin girls from Waukesha in the US, had become obsessed with a website called CreepyPasta, where people can discuss and post horror stories.

Police believe the girls plotted for months to kill one of their classmates so they could become “proxies” of the website’s leader Slenderman.

Chilling details of the girls’ plot were contained in a criminal complaint, which describes how they initially wanted to stab their 12-year-old school friend during a sleepover.

The two girls planned to kill their friend and then walk to a mansion in a national park where they thought Slenderman lived.

The Slender Man is a fictional character that has been attributed to an internet meme created by Something Awful forums user Eric Knudsen (also known as Victor Surge). It went viral and has inspired online fiction known as “creepypasta”, fanart and cosplay.

One of the girls explained to police that just below Slenderman was the killer, just below the killer was the proxy. In order to be a proxy, you have to kill someone to show your dedication to Slenderman.

“Many people do not believe Slenderman is real,” one of the girls told police, and she wanted to prove the sceptics wrong.

The girls plotted to kill a classmate, inviting her over for a sleepover and eventually stabbed her 19 times.

“Based on our investigation, it is believed that the suspects had planned to kill the victim for several months. The Waukesha Police Department is deeply saddened that this 12-year-old girl had to suffer through this horrific crime,” Waukesha Police Chief Russell Jack said.

“One suspect held the victim down while the other suspect stabbed her 19 times in the arms, legs and torso,” he said.

“Many of the stab wounds struck major organs. But, incredibly and thankfully, the victim survived this brutal assault.”

Police Chief Jack said the incident was “a wakeup call for parents”.

“The internet can be full of dark and wicked things. Unmonitored and unrestricted access to the internet by children is a growing and alarming problem.”

According to the complaint, the girls went to Skateland with the father of one of the girls before heading home for a sleepover. Originally the two accused planned to kill the victim about 2am while she was sleeping but this changed.

Instead the girls decided to go to a nearby park the next morning and one of the girls grabbed a knife from the house before they went to the park.

They took the victim to a bathroom in the park but both girls lost their nerve, one apparently said she “couldn’t do it”. Later they decided to play a game of hide and seek in the woods and this was when the stabbing occurred.

One of the girls sat on the victim so the other could stab her, but then they were worried that her yelling would attract attention so they let her up.

Then one of the girls tackled the victim and started stabbing her, before giving the knife to the other girl who also stabbed her.

Afterwards the girls left the scene and walked to Walmart. The victim was able to crawl out of the woods onto a road where a cyclist found her.

Police found the two accused later and recovered the knife from a purse.

Family of one of the accused attended a court appearance on Monday and broke into tears several times during her appearance.

“The family is very horrified at what has happened,” attorney Donna Kuchler said.

On Monday both girls were charged as adults for attempted first degree intentional homicide, if convicted they face 60 years in jail.

Waukesha County District Attorney General Brad Schimel told reporters that he expected attorneys would attempt to “reverse waive” them into juvenile court but he would resist this.

“A prosecutor doesn’t have to charge a 12-year-old in adult court. They could charge an offence that doesn’t have direct adult-court jurisdiction. Given the nature of this particular crime, I just don’t know how we could call it anything other than that,” he said.

If convicted in juvenile court, the girls would be out of jail by the time they were 25.

“Right now, I don’t enough about the psychological make up of these two girls, their history,” Mr Schimel said. “That information just isn’t available to us yet.”

The girls are due back in court on June 11.