Image copyright Police handout

A US teenager convicted of trying to kill her friend in order to please the fictional online character Slender Man has asked for her sentence to be reduced.

Morgan Geyser is serving 40 years in a psychiatric hospital after the near fatal attack in Wisconsin in May 2014.

Along with her classmate Anissa Weier, she lured Payton Leutner into woods and stabbed her 19 times.

Payton managed to crawl free on to a path and survived.

All three girls were 12 at the time.

Grounds for appeal

Geyser stood trial for attempted first-degree intentional homicide in adult court, where crimes that severe are usually heard.

Her lawyers claim that because Geyser believed Slender Man would hurt her family if she didn't kill Payton, she should have instead stood trial for the second-degree version in youth court.

As a juvenile, the 12-year-old would have been locked up for a maximum of three years if found guilty and then supervised until she was 18 but, as it was, the judge gave her the full sentence prosecutors asked for - arguing she was a risk to herself and others.

The appeal also argues that when she agreed to be interviewed by detectives at the time, resulting in her confession, Morgan Geyser wouldn't have been able to understand what rights she had given up.

Doctors gave conflicting opinions on the severity of her mental health and the treatment she needed.

Slender Man

Slender Man is thought to have originated from an internet competition in 2009, which asked for a modern myth that could terrify people.

He's described in fictional stories as an unnaturally tall, thin, demon-like figure that lacks facial features, lives in a mansion in a forest and abducts children.

Authorities say the girls had hoped to live in that fictional home after the attack.

The film Slender Man was released in 2018 based on the story of the character.

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