The gunman in a Colorado high school siege which left one girl dead along with the attacker had sexually abused some of his hostages, police say.
Morrison had a criminal record
Naming the attacker as Denver area man Duane R Morrison, 53, Sheriff Fred Wegener said he did not seem to have links to the school in Bailey.
"He did traumatise and assault our children - I'll only say that it's sexual in nature," the sheriff said.
The victim at Platte Canyon High School was named as Emily Keyes, 16.
Officers stormed the school after more than three hours, at which point the lone gunman reportedly shot one of his two hostages and then himself.
A revolver and a semi-automatic pistol were found on his body, Sheriff Wegener said.
The attacker, who appeared in a classroom just before noon (1800 GMT) on Wednesday, initially took six hostages, all of them girls, but gradually released four of them as he talked to police negotiators.
Other students and staff at Platte Canyon and a neighbouring middle school, which have nearly 800 pupils between them, were evacuated during the siege.
The town of Bailey is only a short drive from Columbine High School, where seven years ago two students killed 13 people before taking their own lives.
'He shot her'
The dead gunman had been living in his car, Sheriff Wegener said.
Emily Keyes, 16, was fatally wounded by Morrison
State records show he had criminal convictions for theft and marijuana possession dating back to 1973 and in July he was arrested for obstructing police in west Denver.
Holed up in a second-floor classroom with his hostages, he had reportedly told the police he had a bomb in his backpack.
Sheriff Wegener said Morrison had made few demands. "Most of the demands were, 'Leave me alone, get out of here'," he added.
When negotiations appeared to be breaking down, a specially trained police Swat team threw a stun grenade and stormed the building.
Morrison apparently turned his gun on himself after firing at police and fatally wounding Emily Keyes.
"We firmly believe, without a shadow of a doubt, that the suspect was responsible for the death of the child," said Joe Morales, executive director for the Colorado department of public safety.
Students at the school said they did not recognise the gunman who appeared to be dressed like a student.
Jessica Montgomery, 15, told AP she had seen the gunman in a second-floor hallway shortly before noon.
She described him as "creepy", saying he had acne and stubble on his face.
Another student at the high school, Cassidy Grigg, went on US television channels NBC and ABC to give an account of how the gunman had chosen his hostages and threatened him personally.
However, the boy's mother, Larina Grigg, later announced that her son had lied, Colorado newspaper The Rocky Mountain News reports.
"Cassidy has never been dishonest in his life but in this matter he wasn't truthful," she said on Thursday afternoon.
"He was not in the room with the kids. He wants to say he's sorry. I know and he knows he made a huge mistake."