SHOCKED staff and pupils in Nebraska are struggling to understand why a 17-year-old boy opened fire at an Omaha high school, killing an assistant principal before shooting himself dead.
An angry online posting on a social networking website has offered few clues about why he turned violent, and as authorities work to sort out what may have led to Wednesday's shooting, those who knew Robert Butler Jr are struggling to reconcile his final actions with their memories of the outgoing student who liked to make jokes and sometimes got into trouble for talking in class.
The gunman, the son of a police detective who had attended Omaha's Millard South High School for no more than two months, also wounded the principal before fleeing the scene and shooting himself in his car.
"It's just unreal," said Butler's step-grandfather Robert Uribe, who said the polite young man he knew did not seem like a likely gunman. "I don't know what would possess him to do that."
Assistant principal Vicki Kaspar, 58, died at Creighton University Medical Centre on Wednesday evening, hours after the shooting. Principal Curtis Case, 45, was in serious but stable condition.
Butler posted a rambling message on Facebook shortly before the shooting but he didn't supply many details. Instead, the expletive-laced note predicted Butler's friends would hear about "evil things" he was about to do.
He wrote that the Omaha school was worse than his previous one, and that the new city had changed him. He apologised and said he wanted people to remember him for who he was before affecting "the lives of the families I ruined". The post ended with "goodbye".
A former classmate from Lincoln, Conner Gerner, recalled Butler as being energetic, fun and outgoing, and who sometimes got in trouble for speaking out too much in class.
Police later revealed that Ms Kaspar had sent Butler home from the school a few hours before the shooting for driving on the football field.