An old Internet meme called “Slender Man” inspired two young Wisconsin girls to stab their 12-year-old friend, police said Monday.

The girls, who are also 12, stabbed their friend Saturday morning and left her injured. She is currently hospitalized in stable condition.

The girls allegedly lured their friend to a wooded area in Waukesha, reports CNN. There, they stabbed her 19 times and left her there, before a bicyclist found her Saturday on a sidewalk, Police Chief Russell Jack said.

The Los Angeles Times reports that the girls’ names are Morgan Geyser and Anissa Weier. They will be charged with attempted first-degree intentional homicide, the Waukesha County district attorney's office said.

Police say that Geyser and Weier planned the murder for months and hoped to impress the “Slender Man,” a fictional character created on the Internet back in 2009 on the Something Awful website. They wanted to prove that the character existed by killing for the “Slender Man.”

The girls said they first encountered “Slender Man” on Creepypasta Wiki. That site features crime stories written for the web that often look like real news items. The site had issued a statement today, expressing condolences to the family of the victim and that they do not encourage violence.

“Unmonitored and unrestricted access to the Internet by children is a growing and alarming problem,” Jack said in a statement, noting that this incident should be a wake-up call for parents. “Parents are strongly encouraged to restrict and monitor their children’s Internet usage.”

Geyser and Weier are being held on individual $500,000 cash bonds. They will be charged as adults and will be in court Monday.