Morgan Geyser and Anissa Weier never found it all that easy to make friends.

The girls lived in the same subsidised housing complex, Sunset Apartments, and caught the bus to and from school together.

Morgan had an angelic face with dimples, framed by long, dark, blonde hair. She wore black rimmed glasses.

She was obsessed with Harry Potter, and was once seen running through the playground at lunch time with her best friend Bella, imagining that Voldemort was chasing them. Otherwise, Morgan’s classmates described her as quiet and mysterious.

Anissa had short, dark hair, unusual for a girl of her age. She had a round face, fair skin and always wore thin glasses.

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She loved online forums, YouTube and her Internet history revealed that she had a dark sense of humour, often posting graphic dead baby jokes.

Since fourth grade, Morgan’s best friend was Payton Leutne, who went by the name ‘Bella’. The pair were inseparable. They both loved cats and rollerblading.

But two years later, when they were 12 years old, Morgan’s friendship with Anissa began to develop.

Anissa didn’t like Bella much, and often referred to her as a “bitch” behind her back. Maybe it was that Bella made friends more easily than Anissa, or that she was envious of her friendship with Morgan. Either way, the two were friendly, but only through Morgan.

The three girls attended Horning Middle School in Waukesha, a suburb of Milwaukee, in America’s north-east. A mother at the school described them as “misfits,” and certainly not “girly girls.” They weren’t at all interested in boys or music.

On May 30th, 2014, Morgan invited Anissa and Bella over for a sleepover to celebrate her 12th birthday. The three visited Skateland, an indoor rollerskating rink, which played top 40 hits.

At 9:30pm Morgan told her dad she’d had enough, and he drove the three of them back to the Geyser home. They played on the Internet for a few hours, before going to sleep – all sharing Morgan’s bed.

The next morning they had donuts and strawberries for breakfast, and then Morgan asked her mum if they could go to the park and play.

The three headed for David's Park, with Bella walking ahead and Morgan and Anissa dropping behind. It was at this moment that Morgan revealed to Anissa what she was hiding under her jacket: a kitchen knife with a black handle.

Moments later the two girls attacked Bella for the first time, pushing her head against the brick wall of a public bathroom. Morgan was, at first, unable to cope with the brutality, allegedly withdrawing from the act and singing to herself. Anissa stroked her, as she described "like a cat", in order to calm her down.

Anissa then suggested they play hide-and-seek, with Morgan counting first. Anissa again tackled Bella, but was unable to hold her down. The two briefly argued over who would commit the act, while Bella played with flowers on her own.

“I’m not going to until you tell me to,” Morgan whispered to Anissa.

Seconds later Anissa said, “Kitty now."

“Go ballistic, go crazy,” Anissa instructed.

"Don't be afraid," Morgan said to Bella as she pushed her. "I'm only a little kitty cat."

Bella was stabbed 19 times, puncturing her arms, legs, liver, stomach and pancreas. Morgan missed a major artery near Bella's heart by just the width of a human hair.

"I hate you! I trusted you!" Bella yelled at the top of her lungs. She attempted to run away, but fell. The two girls then took Bella deeper into the woods, and laid her down, before abandoning her body.

Morgan and Anissa washed themselves of Bella's blood in the nearby Walmart bathrooms. They then set out for the woods, crying and singing.

But, where were they going?

*****

Since the beginning of time, people have told stories about monsters.

There is not a culture on earth that doesn't have it's own version of the boogeyman. We have demons, witches, beasts, goblins and ghosts.

And in the new millennium, the internet gave birth to The Slender Man.

He is tall, thin, faceless and wears a black suit. Slender Man stalks children. Being close to him elicits 'Slender Sickness', which prompts bouts of amnesia, nightmares, coughing, nosebleeds, paranoid behaviour and irrational acts of violence.

Anissa discovered Slender Man online at a time when she felt particularly isolated. She was infatuated by the folk figure.

Around October 2013, Anissa introduced Morgan to Slender Man.

Both girls believed he was real, and desperately wanted to become his "proxies" or followers. They felt that in sacrificing Bella they would prove their loyalty to him, and were afraid that if they didn't, Slender Man would kill their families.

After the 'murder' was carried out, they believed they would come to serve Slender Man and live in his mansion, which in their minds, was located in the Nicolet National Forest.

*****

Bella was left to bleed in a ditch just outside the park where she was stabbed.

Despite her extensive injuries, the 12-year-old managed to crawl to a nearby road and lie on a sidewalk, until a cyclist spotted her and called 911.

She was rushed to hospital, barely able to speak. Bella eventually managed to name one of her attackers.

A mass search ensued for Morgan and Anissa.

Eventually they were found by a police officer, on their way to find Slender Man. The officer found the weapon in a bag carried by one of the girls, and arrested them both.

The girls were separated and interrogated separately by officers.

Anissa wrung her hands in a small room in the police station, unable to sit still. She stared blankly at her odd socks, weeping intermittently. As though she were reciting a mundane day at school, Anissa explained that they believed they would be, "spending the rest of [their] lives," with Slender Man. She told them that during their walk, she had a "total nervous breakdown, and blamed Morgan for everything. I said, 'You stabbed her. You wanted to do this.'"

She was detail-oriented and made it clear it was not her who committed the stabbings - she is far "too squeamish".

Anissa also told the detective that they intended on becoming proxies for Slender Man through blood sacrifice. Bella's potential death would earn them his protection, and then they would live with him in a mansion in the forest, away from their friends and family.

Morgan, on the other hand, said she felt, "surprisingly calm." In fact, she "felt nothing."

She spoke to the police in a monotone, seemingly detached from reality.

At first, she blamed the attack on Anissa. It was her idea. She couldn't remember who actually stabbed Bella, but she did mention Slender Man.

Morgan asked Detective Casey if she'll rot in jail, and begged him not to "cut off [her] head".

He asked her to describe the moment in detail, and Morgan grew increasingly annoyed.

"Stabby stab stab stab," she exclaimed.

"Are you trying to do this over and over again and see if I tell the story differently? I have the right not to go into detail about it if I don't want to," Morgan said to the officer.

One significant distinction came out of the two interviews with Anissa and Morgan.

Anissa appeared aware that Slender Man was a fictional character invented on Creepy Pasta. “Beforehand, I believed,” she told them. “Now I know it’s just teenagers who really like scaring people and making them believe false things.”

To Morgan, however, Slender Man was not a work of fiction.

“It was weird. I felt no remorse … I still have this idea that it was necessary,” Morgan told detectives.

*****

The girls' parents were called to the police station, and after a number of hours were told they could not take their daughters home.

They were being charged with attempted homicide.

"I sobbed. I ran to the bathroom and threw up. It didn't seem possible," Morgan's mother said.

In subsequent interviews the girls' parents have spoken of their struggle to understand what they could have done differently to prevent the online folk legend from taking hold.

“I think ‘surreal’ is the best way to describe it,” Bill Weier, Anissa's father, said. He is terrified about his son's exposure to school-mandated iPads. He feels powerless. Weier says he could not have monitored Anissa's time on the Internet more closely, yet darkness infiltrated their home in a way he never thought possible.

With that said, a search of Anissa's YouTube history revealed that she would often like and comment on videos of mice being tortured by cats.

Morgan's bedroom contained haunting drawings of Slender Man himself and several dismembered Barbie dolls.

Both Morgan and Anissa have been psychologically examined since the stabbing.

Morgan has been diagnosed with schizophrenia, a condition which her father also suffers from. According to Dr Kenneth Casimir, Morgan has a "long history of auditory, visual, and tactile hallucinations," and since the age of three has been haunted by "vivid dreams she wished she could change."

 Morgan has also described feeling ghosts hug her, and of seeing Slender Man all her life.

Dr Casimir determined that Morgan is at continued risk of harming others, as she told him, "If Slender Man told me to break into someone's house and stab them, I would have to do it."

Morgan has also been diagnosed with oppositional defiant disorder.

Anissa has been diagnosed with depression, delusional disorder, and schizotypy, defined as a "diminished ability to determine what is real and what is not real."

Now aged 15, both girls initially pleaded not guilty to attempted first-degree homicide, by reason of mental illness.

Under Wisconsin law, anyone over the age of 10 is automatically tried as an adult. If found guilty, Morgan and Anissa could have been imprisoned for up to 65 years.

In August 2017, in a deal with prosecutors, Anissa changed her plea to guilty for the charge of attempted second-degree intentional homicide. She claimed she was mentally ill at the time of the attempted murder. The plea deal meant she would spend three years in a mental hospital if deemed mentally ill, and 10 years in prison if not.

On Friday 15 September 2017, after 11 hours of deliberations, a jury of 12 people deemed Anissa mentally ill at the time of the attack.

In her closing statements her defence lawyer, Maura McMahon, told the jury Anissa was lonely, depressed, and she had descended into madness.

“This sounds crazy, because it is,” McMahon said. “This was a real being to this child and she needed to protect those around her. At 12 years old, she had no way to protect herself from (Slender Man) except for Morgan’s advice and they swirled down into madness together.”

Morgan's trial is set to begin on October 9 this year.

****

Four months after the stabbing, Bella returned to school. Since her attack, she has received thousands of letters of support from people around the world.

Today, she loves music and sometimes has friends over to her house for sleepovers. She attends weekly therapy sessions with her family.

Slender Man, of course, lives on online.

One of the most common search terms regarding the supernatural creature is "Was Slender Man bullied?" Perhaps he speaks to the young person who feels alienated, misunderstood or even monstrous.

In analysing the case, psychologist Jacqueline Woolley says, “I think the concept of what’s real has always been pretty messy. Technology is creating these new situations in which it’s becoming even messier".

Slender Man began as something harmless enough. He was invented as part of a photoshop contest in 2009, in which users edited everyday photographs to make them appear paranormal. It's recreational terror - intended to scare and excite us.

But as a user named Soakie wrote on an online forum, not long after Slender Man's inception;