The verdict will decide whether Weier will got to a mental hospital or a prison.
A "deluded" schoolgirl helped a friend stab their classmate 19 times so the fictional Slender Man character would not slaughter her family, a court heard. At the time of the incident, all three girls were 12-year-old.
Prosecutors argue Weier knew what she was doing was wrong, but went along with the attack to keep her friendship with Geyser. Her trial is set to begin October 9.
The decision was made after almost a dozen hours of debate between members of the jury. She believed he would hurt her and her family if she didn't help commit murder.
An attorney for a Wisconsin teenager who was found by a jury to have been mentally ill in the stabbing of a classmate says the teen was relieved by the verdict.
Both Weier and Geyser told detectives they felt they had to kill Leutner to become Slender Man's "proxies", or servants, and protect their families from the demon's wrath.
Gregory Van Rybroek, who has worked with youth at the Mendota Mental Health Institute, was the second court-appointed psychologist to testify in Anissa Weier's trial in Waukesha County Circuit Court.
Weier struck a deal with prosecutors in August in which she pleaded guilty to being a party to attempted second-degree intentional homicide. Westendorf testified at Weier's mental capacity trial that she believes Weier suffered from a shared delusional disorder that left her unable to conform her conduct to the law when she and Morgan Geyser tried to kill their friend, Payton Leutner, in 2014.
A jury determined Anissa Weier was mentally ill when she and Morgan Geyser lured Payton Leutner into woods in Milwaukee, United States, in 2014.
Weier's dad William said his daughter went through a hard time after his divorce. "They were compelled to act on the delusions and that makes it a disorder", said Michael Caldwell, psychologist.
Weier's lawyer Maura McMahon said, "Life is better for children when adults around them are in communication with each other".
Slender Man first appeared on the internet in 2009.
"She will have an uphill road", McMahon said. The same number (though not same jurors) voted she was not criminally responsible for her actions.
A shared delusion and an interest in the paranormal led two girls to stab another 12-year-old girl in a Wisconsin park as a tribute to the fictional horror character Slender Man, a psychologist testified Wednesday.