OMAHA, Nebraska -- Authorities Thursday searched for clues as to why a teenager armed with an assault rifle randomly opened fire on Christmas shoppers in a mall, killing at least eight before turning the gun on himself.

"It appears random and the duration of this event only lasted a few minutes," said Omaha Police Chief Thomas Warren.

Robert Hawkins, 19, left a suicide note saying he wanted to be "famous" and a surreal scene of carnage which is becoming familiar.

"The victims and their loved ones are in the prayers of Americans," President George W. Bush said Thursday.

"Our whole nation grieves with the people of Omaha."

The carefree strains of holiday music were suddenly smothered by the sounds of rapid gunfire and screams Wednesday as Hawkins turned his gun on a group of shoppers and store employees on the third floor of an open department store, witnesses said.

And as terrified people hid behind clothing racks and ran for their lives, the youth dressed in a camouflage vest and carrying a black backpack leaned over a railing and shot at people on the escalator and floor below.

He managed to kill eight of the 13 people he shot with an AK-47 assault rifle, which he had stolen from his estranged stepfather.

A troubling portrait emerged Thursday of the disturbed youth who had been a ward of the state and spent time in substance abuse and mental health counseling after he was arrested as a teen.

The high school dropout who had recently broken up with his girlfriend and been arrested for underage drinking on Friday, cracked after he was fired from his job at McDonald's after being accused of stealing 17 dollars.

About an hour before the rampage began, Hawkins called the family who had taken him in after a brief stint on the streets.

He was upset about losing his job, said the woman who took the tall, bespectacled young man into her home in August 2006.

"I told him, 'Well just come on home, we'll talk about it -- it's just not that big of a deal,'" Debora Maruca Kovac told CBS News. "He said it was too late."

Hawkins said he had been a burden to all his friends and family and didn't want to be one anymore. He thanked Maruca Kovac for everything her family had done for him and told her that he had left them a note.

"It said how much he loved his family and all his friends and how he was sorry he was a burden to everybody," she said. It also said that "his whole life he was a piece of shit and now he'll be famous."

While he was obviously depressed, Hawkins had shown no previous signs of violence, she added.

"He came to us like a little lost puppy. Scared and lonely. He wasn't a violent person," she said.
"He was always very sensitive and caring, always wanting to know how everybody was doing."

Most of the people who were mowed down when Hawkins started shooting were believed to be store employees rather than shoppers, US media reported.

Renee Toney was working in the gift wrap area near where Hawkins began shooting. A supervisor shouted at people to go into the nearby stockroom and Toney and the others rushed to it.

"None of them made it out," Toney said. "I was up front, and everybody except me was shot. It's a blur. I don't even know how I got to the stockroom. I was the closest one to the stockroom. Within seconds, they were shot right behind me."

The Nebraska incident was the latest in a series of shootings in the United States, which is home to more than 200 million privately owned firearms for a population of just over 300 million, authorities say.

In February, an 18-year-old Bosnian refugee shot and killed five people in a Utah shopping mall before being gunned down by police.

There have also been a series of school shootings this year, the worst being the Virginia Tech massacre in April, when 32 people were killed by a student who went on a campus rampage.