A Wisconsin judge has refused to release a woman from a mental institute after she brutally stabbed a peer as a child to earn the favor of the fictional horror character Slender Man in a case that shocked the nation a decade ago.

Morgan Geyser, now 21, had requested to be released in January from the Winnebago Mental Health Institute, and proceedings started Wednesday and continued Thursday.

Waukesha County Circuit Judge Michael Bohren on Thursday determined Geyser posed a risk of harming…