Omaha, Nebraska (CNN) -- A Nebraska high school senior had been called out of class to speak with an assistant principal just hours before he returned to school and fatally shot her, Omaha police said Thursday.
Robert Butler Jr., 17, also wounded the school principal and was later found dead of a self-inflicted gunshot wound.
Millard South High School Assistant Principal Vicki Kaspar, 58, died at Creighton University Medical Center several hours after she was life-flighted away from the school with critical wounds. Principal Curtis Case, 43, remains hospitalized at the same facility in serious but stable condition.
In a statement, Omaha Police Lt. Darci Tierney said Butler, the son of an Omaha Police detective, was called out of class to speak with Kaspar shortly after the Wednesday morning session began, apparently to discuss a criminal trespass citation he received on New Year's Day for driving his vehicle on the school's track and football field.
An hour and 15 minutes later, a security guard escorted Butler out of the building, but he returned 3 1/2 hours later and signed in to speak with Kaspar. Tierney said police believe he was in her office for about four minutes before he shot Kaspar and Case. An unarmed security officer, after hearing the gunshots, recognized Butler as he walked out.
Butler pointed his weapon at the security guard, who took cover. Less than an hour later, police got a call about a suspicious vehicle less than two miles away matching the description of Butler's car. They found Butler's body in the still-running vehicle.
Butler's family has extended their "sympathy and prayers" to the families of those affected.
"Our family is shocked and confused about Robert Jr.'s actions," the statement, released by the Omaha Police Department, read. "We want the community to know that we care deeply about the students and staff of Millard South and their families. We thank those who have called for their support in this very difficult time."
Police say the gun used in the incidents belonged to Butler's father, a detective with the Omaha Police Department.
Butler had brief conversations with his father after he was sent home Wednesday morning, but police said there were no signs anything was particularly out of the ordinary.
"All indicators were that he was acting normal," Police Chief Alex Hayes said. "He was disappointed about the discipline, but he was not acting in any kind of manner that he was upset, acting frustrated or angry or anything like that."
Nonetheless, Butler posted a Facebook status update -- prior to returning to the school, Hayes believes -- implying he would be ruining families' lives and apologizing in advance.
"Everybody that used to know me I'm sry," he wrote on his profile, unedited except for the profanity.
"Omaha changed me and f***ed me up and the school I know attend is even worse ur gonna here about the evil s**t I did but that f**kn school drove me to.this I wont u guys to remember me for who I was b4 this ik I greatly affected the lives of the families I ruined but I'm sorry.goodbye."
During the school's lockdown on Wednesday, senior Shelby Piniarski, a friend of Butler's, remembered that when word started to spread that it was Butler, she didn't believe it.
"I kind of was hoping that it was just one of those high school rumors, like 'Oh I know who did it, I know who shot whatever,'" Piniarski said. "But it wasn't. It was real."
It wasn't until she read his post that she gave in to the chatter.
"I got a text message of his Facebook status, and that's about the time my heart broke."
Butler had only been a student at the Omaha school for a couple of months, previously living with his mother in Lincoln, Nebraska.
"We believe that he was having some disciplinary problems with being tardy at school, maybe not listening to Mom -- that kind of thing -- thinking that Dad may be able to help him out better than Mom was," Hayes said. "Hopefully we can come to a point where we think we know exactly what happened."
Hayes said the police department's safety committee will review the incident. The department's firearms policy says that officers "will not store or leave a firearm in any place within the reach or each access of a minor or unauthorized individual."