Robert Hawkins wrote in a three-page note that he 'just snapped', then went on to apologise to his family and friends.

'I know everyone will remember me as some sort of monster but please understand that I just don't want to be a burden on the ones that I care for my entire life,' the teenager wrote.

'I just want to take a few pieces of (expletive) with me.'

The note was released on Friday alongside chilling surveillance video images of the shaggy-haired, bespectacled 19-year-old taking aim at holiday shoppers.

Hawkins was a troubled teenager who spent four years in a series of treatment centres, group homes and foster care after threatening to kill his stepmother in 2002.

He had recently broken up with a girlfriend and lost his job at a McDonald's fast-food outlet.

The note was left at a house where Hawkins lived. He said his friends would be better off without him, and told them to remember the good times they had.

'Just think tho I'm gonna be (expletive) famous,' he wrote.

Hawkins was more apologetic on another page, which was addressed to his family.

'I'm so sorry for what I've put you through I never meant to hurt all of you so much and I don't blame any one of you for disowning me,' he wrote.

'I've just snapped I can't take this meaningless existence anymore. I've been a constant disappointment and that trend would have only continued.'

He added: 'I love you mommy. I love you dad', and expressed love for several others.

Another page was his will: 'I'm giving my car back to my mom and my friends can have whatever else I leave behind.'

Hawkins went to Omaha's Westroads Mall on Wednesday with an AK-47-style rifle.

Surveillance video and still images of the attack show him initially walking into the mall unarmed. He returned to the store six minutes later, according to time-stamps on the video footage.

The video from the department store's south entrance camera shows Hawkins entering the store and immediately walking to the lift to his right. His right hand was pressed against his midsection to hide what police said was the rifle.

Other footage released showed people fleeing the store, and the first police officer on the scene walking in with his gun drawn.

Police did not release a video of the shooting, but released a still image from the tape that showed Hawkins with his sleeves rolled up, aiming the rifle to fire in front of a store mannequin.

He opened fire randomly in the Von Maur store, fatally wounding eight people before taking his own life.

In his apologies to his friends in his note, he said: 'I've been a piece of (expletive) my entire life it seems this is my only option.'

AP