Morgan Geyser, who was living under court-supervised conditions in a Wisconsin group home due to her involvement in the infamous 2014 stabbing of a fellow 12-year-old classmate, was located late Sunday night in Illinois, roughly 150 miles (240 km) from her last known location.

Authorities reported that Geyser went missing Saturday night after she removed her electronic monitoring bracelet, a device meant to track her whereabouts, according to Madison police.

On Sunday, law enforcement officers in Posen, Illinois, responded to a call about individuals lingering behind a truck stop. Upon arrival, they found a man and a woman asleep on the sidewalk, as stated by the police.

When approached by officers, the 23-year-old Geyser initially provided a false identity, according to the Posen Police Department.

“After repeated requests for her identification, she eventually confessed that she was withholding her real name because she had ‘done something really bad,’ further suggesting that officers could simply ‘Google’ her name to find out more,” the police recounted.

Years earlier, Geyser had pleaded guilty to attempted murder in the stabbing of her classmate, Payton Leutner. At the time, they were both 12 years old.

The grisly attack gripped the public’s attention and became the subject of heavy news coverage at the time, raising questions about how parents can keep tabs on everything kids consume online, and how they can be sure their children can truly separate reality from fantasy.

The crime was said to be inspired by the fictitious character Slender Man.

Here’s what we know about the search for Geyser and the internet-created boogeyman that prompted an attack that shocked the nation more than a decade ago.

Slender Man, a menacing, faceless man in a dark suit – sometimes portrayed with octopus-like tentacles – was a crowdsourced internet-created boogeyman that first appeared in an online forum in 2009, according to Shira Chess, an associate professor of entertainment and media studies at the University of Georgia and co-author of the book “Folklore, Horror Stories, and the Slender Man.”

“He falls broadly into a category of fiction that is colloquially referred to as ‘creepypasta,’ or internet legends that have meme-like qualities, typically lack known authorship, and are easily spreadable,” Chess told CNN in an email Sunday.

Many imaginative fans saw Slender Man’s facelessness as a blank canvas in which to reimagine him in any number of ways, Chess added.

Slender Man’s popularity has gone down in recent years, according to Chess, who noted the fandom peaked in the early to mid-2010s.

“I can anecdotally say that he still performs the role of boogeyman on playgrounds,” Chess told CNN.

How did the stabbing unfold?

In May 2014, the trio had gone to Geyser’s home for a slumber party to celebrate her birthday, Leutner previously told ABC. During those times, Geyser constantly talked about Slender Man, she added.

“I thought it was odd. It kind of frightened me a little bit,” Leutner said of her friends’ fascination with the character. “But I went along with it. I was supportive because I thought that’s what she liked.”

As the friendship between Geyser and Weier grew, so did the pair’s fixation with Slender Man, Leutner said. While Leutner didn’t know her friends planned to harm her, something felt off that night in retrospect, she said.

“At all of our past sleepovers, (Geyser) always wanted to stay up all night because she could never do that at home,” Leutner said. “But on (the night of) the birthday party, she wanted to go to bed.”

Her friends later told investigators they had planned to kill Leutner in her sleep that night but then decided to do it the next morning at a nearby park.

When she woke up, Geyser and Weier were downstairs at a computer, so she joined them for doughnuts before heading to the park. They told her the plan was to play hide-and-seek and asked her to lie down under the leaves and sticks as part of the game, she said.

There in the woods, Geyser repeatedly stabbed her with a kitchen knife and she and Weier left her alone in the woods, bleeding and struggling to get help. After she crawled out of the woods, a passing bicyclist found her and called 911.

Leutner was stabbed near her heart, and she was “one millimeter away from certain death,” court documents said.

When the bicyclist found her, the girl pleaded, “Please help me. I’ve been stabbed,” audio from the 911 call revealed.

At age 15, Geyser pleaded guilty to a charge of attempted first-degree murder in a deal with prosecutors to be placed in a mental institution instead of serving jail time.

Weier pleaded guilty to attempted second-degree homicide due to mental illness or defect as part of a plea agreement. She was committed to 25 years in a mental hospital, The Associated Press reported, but was released in 2021 on condition she live with her father and wear a GPS monitor.

At her sentencing in 2018, Geyser apologised to Leutner and her family.

“I never meant this to happen,” a tearful Geyser said. “I hope that she is doing well.”

Authorities have not identified the acquaintance – who they say was taken into custody – but Posen police told The Associated Press he is 42 years old, was charged with criminal trespassing and obstructing identification and has since been released.

Geyser’s attorney, Tony Cotton, had earlier urged the 23-year-old to turn herself in immediately, saying in a statement: “We worked too hard to secure her freedom for her to continue on this path.”

Prosecutors attempted to block her release, alleging she has been quietly reading gory novels and communicating with a man who collects memorabilia from murderers, but a Waukesha County Circuit judge ordered her release after state and county health officials completed a community supervision and housing plan.