Weier, 13, and her friend Morgan Geyser were arrested after allegedly stabbing their friend 19 times and leaving her in the woods.
In the video, the then-12-year-old told a police officer she believed she had to kill or else the “Slender Man” would "kill my whole family in three seconds."
Detectives also relayed some graphic testimony about the victim's condition, also 12 at the time of the alleged attack, and the stabbing episode.
Both Weier and Geyser have been charged with one count of first-degree intentional attempted homicide but Weier's defense attorney, Anthony Cotton, argued in court she should instead face a second-degree attempted homicide charge in juvenile court, according to The Associated Press. In Wisconsin, juveniles who are charged with the most heinous crimes are automatically sent to adult court. It is then up to the defendant to obtain a “reverse waiver” ruling from a judge that could sent the case to juvenile court.
Weier and Geyser have not entered pleas.