A man who stabbed 20 of his fellow classmates and a security guard at his Pittsburgh-area high school three years ago pleaded guilty Tuesday, the AP reported. Alex Hribal, who was 16 at the time of the attack, pleaded guilty to 21 counts of attempted homicide and aggravated assault, and an additional weapons charge. All of his victims survived the attack and have since recovered. Hirbal “worshipped” the Columbine High School killers, according to psychiatrists for the defense and prosecution, and purposefully attacked the school on the birthday of one of the killers since the school was not in session on the 15th anniversary of the 1999 massacre. The defense had initially hoped to have Hribal declared legally insane, but this request was denied last year. Westmoreland County District Attorney John Peck said he plans to argue for a 30 to 60 year sentence, rather than the 800 years in prison Hribal could receive if given the maxium sentence.