OMAHA, Nebraska (Reuters) - A 19-year-old school dropout who shot and killed eight people and himself at a Nebraska shopping mall smuggled a stolen assault rifle into the building wrapped in a sweatshirt and opened fire without warning when he got out of a third-floor elevator, police said on Thursday.

Robert Hawkins left text and voice messages with friends and family before Wednesday’s bloodbath. “He had apparently been experiencing some mental health problems, ideations of suicide,” Omaha Police Chief Thomas Warren told a briefing.

His victims ranged in age from 24 to 66. They included two male customers and another man and four women who were employees of the Von Maur department store where most of the carnage occurred.

Warren said Hawkins fired more than 30 rounds from the assault weapon.

“It appears that the shooting victims were randomly selected” with little if any words exchanged between the shooter and his victims, the chief said. He killed one mall customer by shooting from the third to the second floor of an atrium but the rest of the victims were mostly store employees in a customer service area.

Four other people were wounded, two of whom remain in critical condition, Warren said. A fifth person suffered a medical problem during the incident and was taken away for treatment.

Warren said a review of security tapes and interviews revealed that unarmed mall police were aware that Hawkins had entered the Von Maur store on the second floor of the Westroads Mall. He quickly took an elevator to the third floor and began firing when the elevator door opened, he said.

Warren said the tapes seem to show that Hawkins had the gun wrapped in a hooded sweatshirt. He said the gun was stolen from the boy’s stepfather. Investigators had not determined if the weapon’s owner had acquired it legally, he said.

The Omaha World-Herald reported in Thursday’s editions that Hawkins had recently lost both his job and his girlfriend and felt worthless.

“I’m a piece of shit,” said a suicide note he left behind “but I’m going to be famous now,” the newspaper said.

Hawkins had been living since last year with the family of a teenage friend who’s mother said Hawkins had shown her family the rifle the night before the shootings. She thought it was too old to be functional.

The newspaper reported that Hawkins’s parents divorced when he was 3 and he had spent time in foster care. He had also broken up with a girlfriend recently and was fired from a fast food restaurant after being accused of stealing $17.

The friend’s mother said he appeared to be trying to turn his life around. When she heard about the mall shooting, she told the newspaper, “I thought ‘Oh, my God, I hope this is not Robbie.” It was then she found the note he had left, which included a will.

Slideshow ( 10 images )

“Our entire state is grieving,” said Nebraska Governor Dave Heineman. Local media said it was the worst single day of violence in the state’s history.

It was the latest in a series of mass killings that have shocked the United States, where gun ownership is widespread and the right to possess arms is a fiercely contested constitutional issue currently on the agenda of the Supreme Court.

The White House said it was a “terrible tragedy.”