Duane R. Morrison, 53, walked inside the school with two handguns and a backpack that he claimed contained a bomb. Investigators did not say what was in the backpack.
Sheriff Fred Wegener announced Friday morning that Morrison had sent a suicide note to a relative in Colorado. He did not reveal the contents of that note, pending its analysis, but did say investigators discovered the note's existence after one of Morrison's weapons was traced to a family member.
During the siege, Morrison released four hostages. While still holding two girls, he cut off contact with deputies and warned that "something would happen at 4 o'clock," authorities said.
About a half-hour before the deadline, a SWAT team used explosives to blow a hole in a classroom wall in hopes of getting a clear shot at him. When they couldn't see him through the gap, they blew the door off the hinges to get inside, said Lance Clem, a spokesman for the state Department of Public Safety.
Morrison fired at the SWAT officers, shot Keyes as she tried to run away and then killed himself, authorities said. During the gun battle, police shot Morrison several times, they said.
"You know, I hold Emily — the responsibility for Emily in my heart and I will live with that for the rest of my life," Wegener, who ordered the SWAT assault, said Friday on CBS News' The Early Show.
Wegener said he was finally able to meet with Keyes' family Thursday afternoon.
"They were surprisingly supportive of everything I've done. But still, it's something that, you know, I will replay over and over," he told Early Show co-anchor Harry Smith.
"In memory of Emily we would like everyone to go out and do random acts of kindness, random acts of love to your friends or your neighbors or your fellow students because there is no way to make sense of this," Louis Gonzalez, a spokesman for the family, said. "It's what Emily would have wanted."
As the hours dragged by, standing among the desperate parents outside the school was John Keyes, wondering about the fate of his 16-year-old daughter, Emily.
Gonzalez said the father had just bought Emily and her twin brother cell phones for their 16th birthdays. As he stood near the school, he searched for a volunteer to send a text message to Emily.
"How are U?" it asked.
At 1:52 p.m., Emily messaged back: "I love U guys."
Less than two hours later, Emily was dying from a gunshot wound to the back of her head.
Authorities said they knew of no connection between Duane Morrison and the hostages he held for four hours Wednesday.
"A male high school student was approached by a suspect (Wednesday) and asked about the identity of a list of female students," Sheriff Fred Wegener said Thursday, later adding that he wasn't sure if it was a written list or names rattled off by Morrison.