The Madison Police Department received confirmation that Morgan Geyser, 23, was taken into custody in Illinois at approximately 10:34 p.m.
“If you see Geyser, please call 911,” the alert said, adding that she had cut off a “Department of Corrections monitoring bracelet.”
Geyser had been living in the group home since earlier this year, when she was granted conditional release from the Winnebago Mental Health Institute. She was committed to the psychiatric facility in 2018, after pleading guilty to attempted first-degree intentional homicide, as part of an agreement with prosecutors to avoid prison time.
Her attorney, Tony Cotton, said on Sunday he had no information about what led to her disappearance but made a direct appeal for her to surrender.
The girls later told investigators they believed they needed to kill their friend to become servants of Slender Man, a fictional horror character. They said they feared he would hurt their families if they didn't go through with the attack. The two had plotted the murder for five months before carrying it out.
Slender Man began as an internet creation in 2009 when Eric Knudsen digitally inserted a mysterious tall figure into ordinary photographs of children. The character evolved into a widespread online phenomenon, appearing in video games, web stories, and eventually a 2018 film.
Geyser's mother, Angie Geyser, told ABC News' "20/20" in 2018 that she was blindsided by her daughter's actions.
"I couldn't believe what I was hearing," she said. "I never would have imagined that my daughter was capable of hurting another person."
She recalled that Morgan had shared some Slender Man stories with her family, but said she hadn't been alarmed at the time. "When I was Morgan's age, I was reading Stephen King novels," Angie Geyser told the program.
Weier also pleaded guilty to attempted second-degree intentional homicide but was found not guilty by reason of mental disease or defect. She was ordered to spend 25 years in a mental health facility, but was released in 2021.
Geyser faced similar charges and received the same finding of not guilty by reason of mental disease or defect.
The Madison Police Department said it was notified of Geyser's disappearance on Sunday morning.