The two girls are accused of stabbing a friend, Payton Leutner, 19 times at a park.
In the first morning of jury selection Monday, Waukesha County Circuit Judge Michael Bohren dismissed 24 from the initial group of potential jurors, United States media reported. "Anissa was under the command and control of a delusional disorder". She described the supposed creature, who was extremely tall, had no face, and could grow tendrils from his back.
"He could easily kill my whole family in three seconds", she told the detective. A passing bicyclist found her.
Her legal team wants to prove that she wasn't responsible for what she did.
Geyser, during her own police interview, claimed it was Weier who jumped on Leutner and "held her to the floor".
Although Weier did not physically stab Leutner, in her mind she knew it had to be done, Smith told jurors. Another girl, Morgan Geyser, is also accused in the attack. Szczupakiewicz argued she wasn't even aware of that until after the stabbing. Osborne says the initial plan was for Weier to stab Leutner, but Weier couldn't do it and instead directed Geyser to do the stabbing. "Go berserk", was the command, Mr Osborne said.
'They knew this was wrong. The victim suffered serious injury and the other girls clearly needed guidance that they didn't get, she said.
They said they were unaware of her obsession with the sinister fictional character beforehand and revealed that their daughter was "absolutely" remorseful over the attack. With Geyser, Weier developed a "delusional belief system" and together they made a plan to kill Leutner and become Slender Man's proxies, Smith said.
Geyser has pleaded not guilty to attempted first-degree intentional homicide. Weier struck a deal with prosecutors in August in which she pleaded guilty to being a party to attempted second-degree intentional homicide, essentially acknowledging she committed all the elements of the offense.
CREEPY CHARACTER: Who is the Slender Man?
The character is understood to have originated in a Photoshop contest on the forums of comedy website Something Awful in 2009.
Jury selection will begin Monday, and Waukesha County Judge Michael Bohren has set aside up to two weeks for the trial.
Knudsen's intention was to "formulate something whose motivations can barely be comprehended, and [which caused] unease and terror in a general population".
It then went viral, with numerous works of fan art and short scary stories - known as "creepypasta" - published online.
The character, which is sometimes said to have long tentacle-like arms to capture prey, stalks children and depending on interpretations can cause memory loss, insomnia and paranoia. Her trial, which began Tuesday, will determine whether was suffering from mental illness at the time of the stabbing and therefore not criminally responsible.
Waukesha County Assistant District Attorney Kevin Osborne told jurors during opening statements that Weier and Geyser knew that they were committing a crime.
Psychologists testified in pre-trial hearings that Weier suffered from depression and a delusional disorder that made it hard to tell reality from fantasy, according to U.S. media. Instead, the 16 jurors - the standard 12 plus four alternates - will be tasked with determining if Weier is mentally ill.
Last month, Weier pleaded guilty to a lesser charge. At one point, Anissa wiped away tears as her attorney recounted how she came to believe Slender Man was real.
ANOTHER STORM BREWING Hurricane Jose 2017 tracker - latest path, where is it, what category is it and how does it compare?
Diamond Offshore Drilling, Inc. (DO) Bond Prices Rise 1.1%
The stock of Diamond Offshore Drilling Inc (NYSE:DO) earned "Sector Perform" rating by RBC Capital Markets on Tuesday, November 3. The Firm offers a portfolio of CRM BPO services, including customer care, sales, collections, back office and technical support.
Foo Fighters Announce Plans To Launch Pop-Up Pub
The Foo Fighters have announced they will open a pop-up pub on Friday for the launch of their new album, Concrete And Gold . Concrete and Gold is the group's ninth studio album and it features both Paul McCartney and Justin Timberlake .