One of the two girls, Morgan Geyser, accused of attempting to sacrifice a classmate in a ritual connected to the Slender Man video game and internet meme will plead not guilty by reason of insanity, according to her attorney.

What happened in the woods of Wisconsin?

According to investigators, the girls, Geyser and classmate Anissa Weier, who were both twelve at the time of the incident, plotted for months over an incident in May 2014 in which they attempted to murder a classmate. The victim had received nineteen stab wounds, across herarms, legs and torso, after being led into the woods near the city of Waukesha, although she eventually survived the incident after being found crawling through the woods by a cyclist, according to reports, and has now returned to school.

Reportedly, the girls had originally intended to perform the ritual at a sleepover party.

Although both girls are currently minors at the age of 14, they will be tried as adults due to the fact that the murder attempt was both premeditated and violent. That said, lawyers have attempted to try the girls in juvenile court.Weier had previously pleaded not guilty last year. According to reports, Geyser will now be evaluated by two court-appointed doctors to see how justified her claim of insanity is.

Just who is this Slender Man?

Investigatorsfound that the attempted murder was part of a ritual meant to please the fictional video game character, Slender Man; the two girls reportedly wanted to become his “proxies.” In fact, the girls had planned to find the character’s mansion, which they believed to exist within Wisconsin's Nicolet National Forest, after the attack.

The character of Slender Man first appeared online in 2009. The Florida-based Eric Knudsen developed the character for the SomethingAwful forum, posting a picture of the figure behind a group of people. Normally portrayed as a white pale creature with a featureless face and black tentacles, the figure soon took a life of his own as an internet meme, eventually gaining his own popular computer game.

A trailer for the game can be seen below.

According to reports, the girls became fascinated with the Slender Man figure after reading a “creepypasta,” an online story that works as an urban legend, about the figure.