Las Vegas gunman Stephen Paddock transferred $US100,000 overseas in the days before the attack and placed a camera in a food cart outside his hotel room to warn him of approaching police.

Paddock killed 59 people and wounded more than 500 others at the Route 91 Harvest Festival after he opened fire in the largest mass shooting in modern US history.

Las Vegas Sheriff Joe Lombardo said he was “absolutely” confident authorities would find out what set off Paddock, a retired accountant who killed himself before police stormed his 32nd-floor room at the Mandalay Bay Resort and Casino.

Police have since found 23 firearms in the 64-year-old’s suite and 19 at his home at a retirement community in Mesquite, Nevada.

Investigators also found explosives in his home and ammonium nitrate (used as a bomb ingredient) in his car.

Photos leaked to US media purporting to show Paddock’s room after he took his own life show guns and ammunition littering the floor. They also appeared to show a note left on a table.

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Investigators are analysing Paddock’s computer and mobile phone, and examining surveillance footage from the Mandalay Bay Casino.

They also want to interview his Australian girlfriend, Marilou Danley, 62, who moved from the Philippines to Queensland in the 1980s.

Paddock transferred $US100,000 ($A127,700) to the Philippines in the days before the shooting, a US official briefed by law enforcement said on condition of anonymity.

Investigators were still trying to trace that money and also looking into a least a dozen reports in recent weeks that said Paddock gambled more than $US10,000 a day, the official said.

The cameras Paddock set up at the Mandalay Bay were part of his extensive preparations that included stockpiling nearly two dozen guns before opening fire from his perch on the closing night of a three-day country music festival below.

“I anticipate he was looking for anybody coming to take him into custody,” Sheriff Lombardo said.

During the rampage, a hotel security guard who approached the room was shot through the door and wounded in the leg.

The firearms found in the hotel had calibres ranging from .308 to .223, and a handgun was also among the weapons.

“The fact that he had the type of weaponry and amount of weaponry in that room, it was pre-planned extensively, and I’m pretty sure he evaluated everything that he did and his actions, which is troublesome,” the sheriff said.

Ms Marilou is considered “a person of interest” and has been speaking with police from the Philippines, where she is travelling. She will be brought back to the US by the FBI.

The gunman checked into Mandalay Bay hotel room using Danley’s ID.

Who was Stephen Paddock?

The wealthy 64-year-old retiree was a keen gambler with a hunting and pilot’s licence, whose father was on the FBI’s Ten Most Wanted list.
Some of the rifles in the hotel room appeared to have been modified in an attempt to convert them into machine guns.

Paddock could also have illegally converted semi-automatic rifles into fully automatic guns, a process made easier by the presence of guides uploaded to the internet.

Chris Sullivan, the owner of the Guns & Guitars shop in Mesquite, issued a statement confirming Paddock was a customer who cleared “all necessary background checks and procedures”, and said his business was cooperating with investigators.

“He never gave any indication or reason to believe he was unstable or unfit at any time,” Mr Sullivan said. He did not say how many or the kinds of weapons Paddock had purchased.

A “bump-stock” is a device that attaches to a weapon to speed up fire. Photo: AP

Clark County Sheriff Joseph Lombardo said investigators knew a gun dealer had come forward to say he had sold weapons to the suspect, but it was not clear if he was referring to Mr Sullivan.

He said police were aware of “some other individuals who were engaged in those transactions”, including at least one in Arizona.

In his Mesquite home police found the explosive tannerite, which can be bought commercially. In his car, police also found ammonium nitrate, which can be used to make bombs.

Police have also searched a home in northern Nevada but have not revealed what they retrieved from the house.

Gunman had ‘bump-stock’ device that could speed up fire

Paddock had two “bump-stocks” that could have converted his semi-automatic guns in fully automatic ones.

The devices have attracted scrutiny in recent years from authorities.

California Senator Dianne Feinstein long rallied against them and several years ago told The Associated Press she was concerned about the emergence of new technologies that could retrofit firearms to make them more automatic.

“This replacement shoulder stock turns a semi-automatic rifle into a weapon that can fire at a rate of 400 to 800 rounds per minute,” she said.

A semi-automatic weapon requires one trigger pull for each round fired. With a fully automatic firearm, one trigger pull can unleash continuous rounds until the magazines are empty.

Numerous attempts to design retrofits failed until recent years when bump stocks came on the market.

-with ABC, AAP