Teen that stabbed friend to impress 'Slender Man' is sentenced to 25 years in a psychiatric hospital

Anissa Weier, one of two Wisconsin girls who tried to kill a classmate to win favour with 'Slender Man', is led into the court for her sentencing hearing. Photo / AP

One of two teenage Wisconsin girls who repeatedly stabbed a classmate to impress a mythical online character named Slender Man was sentenced December 21 to 25 years in a psychiatric institution - the maximum punishment possible, according to the Associated Press.

Annissa Weier, now 16, pleaded guilty in August to second-degree attempted intentional homicide in a deal with prosecutors but claimed she was mentally ill during the attack and not responsible for her actions.

Before her sentencing, Weier apologised, according to the AP.

"I do hold myself accountable for this and that I will do whatever I have to do to make sure I don't get any sort of delusion or whatever again," Weier said. "I want everybody involved to know I deeply regret everything that happened that day. I know that nothing I say is going to make this right and nothing I say is going to fix what I broke."

The case drew national attention in 2014 because of the age of the victim and attackers - all just 12 at the time of the stabbing - and their peculiar motive. Morgan Geyser and Weier lured their classmate, Payton Leutner, into the woods in a Milwaukee suburb after a slumber party. There, Geyser stabbed Leutner 19 times with Weier's encouragement.

The attackers both told detectives they needed to kill Leutner to become proxies, or servants, to Slender Man, a demonlike creature they read about online who is often depicted as a spidery figure in a black suit with a featureless white face. The girls said they were compelled to kill to protect themselves and their families from the demon, and after the slaying planned to run away to the demon's mansion, which they believed was in the Nicolet National Forest in Wisconsin.

Geyser and Weier were both originally charged with attempted first-degree intentional homicide, which carries a possible sentence of up to 65 years in prison.

Leutner survived the stabbing after crawling out of the woods, where a bicyclist found her and called 911. Leutner was raced to the hospital, where the surgeon who operated on her told ABC's David Muir that the knife had nearly penetrated her heart, missing it by less than a millimetre. Damage to Leutner's diaphragm forced her to use pen and paper to communicate for two days after the surgery because speaking hurt too much.

No one from the Leutner's family addressed the court during the sentencing hearing. A letter from Leutner's mother, Stacie Leutner, was read instead. In it, she detailed her daughter's trauma: how her daughter for months slept with scissors under her pillow for protection and keeps her bedroom windows closed and locked. Leutner fears for her life, her mother wrote.

"She will struggle with the events of that day and physical and emotional scars it left for the rest of her life," Stacie Leutner wrote.

The mother wrote that her daughter wouldn't feel safe if her attackers were released without supervision, and that her daughter "deserves to be allowed to heal in an environment where she feels safe."

Geyser, who stabbed Leutner, will be sentenced in February, according to AP. She pleaded guilty to first-degree attempted intentional homicide and claimed she isn't criminally responsible and should not go to prison. Prosecutors will argue for a sentencing of 40 years in a psychiatric hospital.