WASHINGTON (AFP) - Las Vegas mass killer Stephen Paddock was a compulsive player of video poker who took the anxiety drug Valium, CNN reported on Monday (Oct 9).

The report gave new details about the background of the 64-year-old who, on Oct 1, gunned down 58 people and wounded almost 500 for reasons which investigators still have not been able to fathom.

Paddock said in a 2013 court deposition that he was "the biggest video poker player in the world", according to CNN, which obtained a copy of the 97-page document.

The deposition has been turned over to the Federal Bureau of Investigation, the news network said.

It was part of a civil lawsuit against the Cosmopolitan Hotel, where he slipped and fell on a walkway in 2011.

"Nobody played as much and as long as I did," Paddock said, adding that in 2006, he gambled on average "14 hours a day, 365 days a year".

"I'll gamble all night," he said, in what CNN called the first account of his life in his own words. "I sleep during the day."

Paddock, at times, seemed to come off as arrogant and sarcastic during the deposition, according to CNN.

When he gambled, he rarely drank alcohol, his testimony said, because "at the stakes I play, you want to have all your wits about you, or as much wit as I have".

In another development, the sheriff of Las Vegas Joseph Lombardo told reporters on Monday that a security guard who was injured by Paddock was, in fact, shot six minutes before the gunman opened fire on the crowd.

Security guard Jesus Campos was previously hailed as a hero and credited with stopping the assault on the concert crowd by turning the gunman's attention to the hotel hallway.

The new revelation raises questions about why police could not locate Paddock sooner - and indeed why he ended his attack.

SWEAT PANTS, FLIP-FLOPS

Paddock, who police say committed the worst mass shooting in recent US history, owned numerous properties and had no known associations with political, radical or hate groups.

In his court statement, he said he won "from US$100 (S$136) to US$1,350" each time he pushed the button on a gambling machine, wagering perhaps a million dollars a night, CNN said.

Paddock stated that for him, that was not a lot of money.

He said he split his time between California, Nevada, Texas and Florida, travelling at one point "maybe upwards of three weeks out of a month".

As a high-roller, he often lived at the casinos where rooms were provided free "95 per cent of the time", and where he wandered about in black Nike sweat pants and flip-flops, Paddock said.

In spite of his wealth, he carried his own drinks into the high-rollers' area because he did not want to tip the waitresses too much.

Paddock stated in the court deposition that he had no mental health problems, no history of addiction and no criminal record, although he was prescribed Valium "for anxiousness" by a physician to whom he had "good access".

In the deposition, he also provided some biographical information, saying he grew up in California, attended high school in the Sun Valley section of Los Angeles, and college at what would become Cal State Northridge.

Paddock worked for a time as an Internal Revenue Service agent, then began to invest in real estate, CNN reported.

There was no discussion of guns in the court deposition, except for Paddock's confirmation that he had a concealed weapons licence in Texas.

Paddock, who described himself as "happy-go-lucky", lost his lawsuit against the Cosmopolitan Hotel, CNN said.