The police officers who first stormed the hotel room where Las Vegas gunman Stephen Paddock carried out America's biggest massacre in history have broken their silence.

In an interview airing on 60 Minutes in the US, three police officers who were in the Mandalay Bay hotel room will reveal new details about what they discovered.

CBS reports that they found a note in the hotel room that included handwritten calculations about where he needed to aim to maximise his accuracy and kill as many people as possible.

Las Vegas gunman Stephen Paddock's motive has not been determined yet. Photo / AP
Las Vegas gunman Stephen Paddock's motive has not been determined yet. Photo / AP

The officers being interviewed were the first to see Paddock's body and his massive arsenal of weapons and ammunition he had stockpiled for days before his mass shooting, news.com.au reported.

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He requested an upper-floor room overlooking the festival, stockpiled 23 guns, a dozen of them modified to fire continuously like an automatic weapon, with a bump stock device.

He had also set up cameras inside and outside his room to watch for approaching officers.

Officer Dave Newton from the Las Vegas Police Department's K-9 unit said he noticed a note on the shooter's nightstand.

He said the note was located near one of the windows that Paddock had smashed with a hammer to fire onto the crowd at the Route 91 Harvest Music Festival.

Inside shooter Stephen Paddock's room at the Mandalay Bay hotel, Las Vegas. Photo / Supplied
Inside shooter Stephen Paddock's room at the Mandalay Bay hotel, Las Vegas. Photo / Supplied

"I could see on it he had written the distance, the elevation he was on, the drop of what his bullet was gonna be for the crowd," Newton said.

"So he had that written down and figured out so he would know where to shoot to hit his targets from there."

Stephen Paddock's room and the note he left. Photo / Mike Tokes / Twitter
Stephen Paddock's room and the note he left. Photo / Mike Tokes / Twitter

Paddock's hotel suite was on the 32nd floor of the hotel.

Newton told reporter Bill Whitaker recalled how they entered the room amid the flashing lights of a fire alarm set off by an explosive used to blow through the door.

"Very eerie. Yeah, the dust from the explosive breach. And then you have the flashing lights," Newton said. "And that looked straight, like, out of a movie, you know?"

Paddock's hotel suite gave him an ideal perch from which to carry out his attack on a crowd of more than 20,000 people attending the festival concert across the street, some 365 metres away.

The note has not shed any light on the gunman's motives, which authorities are yet to uncover nearly a week after the deadliest mass shooting in recent US history.

GUNMAN WENT TO MIDDLE EAST

Stephen Paddock visited the Middle East on a cruise within the last year, a police source has said.

The anonymous official confirmed the gunman had travelled on a dozen voyages over the past few years - one of which was to the region.

Police had earlier dismissed three claims by Middle Eastern terror group ISIS that Paddock carried out the attack on its behalf after converting to Islam six months ago.

Las Vegas shooter Stephen Paddock (right, black shirt) sharing a meal with Marilou Danley's family in Manilla in 2013.
Las Vegas shooter Stephen Paddock (right, black shirt) sharing a meal with Marilou Danley's family in Manilla in 2013.

But an anonymous police source last night told Associated Press that investigators are closely analysing the cruises he took in the years leading up to the massacre.

Among popular cruise destinations in the Middle East are Dubai and Abu Dhabi, Oman, the Jordanian port of Aqaba, Bahrain, Qatar and a number of Egyptian ports.

ISIS 'RARELY CLAIM' ATTACKS THEY AREN'T INVOLVED IN

The Sun reports how on ISIS expert believes it is plausible that Paddock was in contact with ISIS.

Rukmini Callimachi, a reporter with The New York Times who covers the fanatics for the influential newspaper, said IS's claim carried weight.

She said: "ISIS has rarely claimed attacks that were not by either their members or sympathisers.

"I don't buy the argument that they are now opportunistically claiming attacks to deflect from battlefield losses."

Fifty-eight people were killed and more than 500 injured when Paddock pumped thousands of bullets into a musical festival crowd from the nearby Mandalay Bay Hotel.

Thousands flee as Stephen Paddock sprayed bullets at a crowd of concert goers killing 58 people and leading close to 500 injured. Photo / Getty
Thousands flee as Stephen Paddock sprayed bullets at a crowd of concert goers killing 58 people and leading close to 500 injured. Photo / Getty

He fired into the crowd using his arsenal of more than 20 assault rifles and killed himself shortly before police burst into his room.

Publicly, investigators have said they are struggling to establish a motive for the massacre.

POLICE SAY THEY HAVE NO MOTIVE FOR MASSACRE

Police in Las Vegas said yesterday they have looked at "everything" in Stephen Paddock's life and can find no motive for what drove him to commit America's deadliest mass shooting.

Saying they could find "no known nexus" to suggest Paddock was acting on behalf of Islamic State, Las Vegas police confirmed he was alone in room 32135 of the Mandalay Bay casino when he opened fire last Sunday night.

A lawyer for Paddock's Australian partner, Marilou Danley said she "continues to co-operate fully with the investigation".

"She does not anticipate making any public statements today or in the immediate future," he said.

Clark County Undersheriff Kevin McMahill yesterday expressed the frustration of police and FBI officers who have "run down well more than 1000 leads in this investigation".

"Some of it has helped create a better profile into the madness of this suspect but we do not still have a clear motive or reason why," said Sheriff McMahill.

"In the past, terror attacks or mass murder cases, motive was made very clear by a note that was left by a social media post, by a telephone call that was made.

"Today, in our investigation, we don't have any of that uncovered. I wish we did."

He issued an appeal for anyone with any clues to come forward.

"We do not clearly have a motive or a reason why," he said.

"I can assure we are aware of all aspects of this case to include the rumour, innuendo and suppositions by many in the public.

"And I get it. We all want answers."