A gunman who took over a high school classroom last fall held his gun to the heads of some students as he sexually assaulted them, investigators said in a final report that contained chilling details not previously released.

Duane Roger Morrison, a 53-year-old drifter, screamed and waved a handgun at his sobbing hostages at Platte Canyon High School, fired once into the air and threatened to blow up the building, according to the Colorado Bureau of Investigation report on the Sept. 27 standoff.

Morrison shot and killed Emily Keyes, 16, as a SWAT team stormed the classroom after a four-hour standoff. Five other hostages had already been released, and a sixth escaped as officers entered the room. Morrison died of a self-inflicted gunshot wound, though officers also shot him three times.

The latest report also said Morrison took seven girls hostage; authorities earlier said six.

He held guns to the heads of some female students as he sexually assaulted them and threatened to kill them if they resisted, the report said.

Authorities also released a copy of the suicide note Morrison sent to a brother in Colorado the day of the attack. In it, Morrison said he had been mentally and physically abused as a child but gave no details. He said he began having suicidal thoughts when he was 21 and had trouble controlling his "thoughts and urges."

"I have no idea what's real and what's not real," he wrote.

Early in the crisis, deputies rushed to Room 206 and ordered Morrison to drop a handgun he was holding to a student's head. Morrison refused and told deputies he had three pounds of plastic explosives, the report said.

"Think what that would do to the school," he said.

During the standoff, Morrison erupted in "sporadic fits of rage, periodically screaming at the remaining hostages," the report said.

Although Morrison sometimes spoke to the deputies, out of view in the hall, he eventually required the hostages to call out his messages, the report said.

Morrison ordered a teacher to leave the room, and she complied after he said he had an explosive device and threatened violence to the students if she didn't, the report said. Investigators later found no explosives.

No details of the sexual assaults will be released because of state privacy laws, said Prak County Attorney Steve Groome.