Law enforcement have said they are 'confident' Stephen Paddock carried out the Mandalay Bay massacre from his hotel room alone.

Las Vegas Metropolitan Police Department Undersheriff Kevin McMahill said on Friday that investigators are sure no one else was in the room before he shot dead 58 and injured almost 500 on Sunday.

Earlier, NBC News had reported a mysterious charger that did not mach any of Paddock's cellpones - raising the possibility that another person had been with Paddock beforehand.

Police are still looking into whether gunman Stephen Paddock (above with girlfriend Marilou Danley in 2013) had an accomplice who helped him plot his attack or knew about it

However, later police said that they have now matched all the cell phones and all the chargers and that they belong to Paddock.

'We're very confident there was not another shooter in that room,' said McMahill during a press conference in Las Vegas on Friday afternoon.

'What we cannot confirm is whether anybody else knew about this incident before he carried it out.'

This comes as local and federal officials announced they are erecting billboards around the city appealing to the public to come forward with information about the shooting.

The billboards will have the message 'If you know something, say something' and investigators hope this will help generate leads for the case which has so far left law enforcement struggling to find a motive.

'There are still a number of people out there that know that something looked out of place,' said McMahill

'Someone may have been acting suspiciously that night, or in the years prior, the months prior. Someone that may have seen something or knows something.'

The FBI's special agent in charge in Las Vegas said that the idea is to reach 'as many people as we possibly can' and that they will not stop until 'they have the truth'.

At a press conference on Friday, Las Vegas Metropolitan Police Undersheriff Kevin C. McMahill said they were no closer to establishing a motive for the mass murder

But at the press conference on Friday, McMahill said detectives were no closer to understanding what motivated Paddock's killing spree.

'To date we have run down well more than 1,000 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.

'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 confirmed that Paddock was the only gunman, as suspected, and said there was no proof that anyone else accessed the room in the days before the attack.

Authorities are however still investigating whether someone knew Paddock was about to commit the worst mass shooting in US history.

The only other named person of interest is Paddock's girlfriend, Marilou Danley, who was in the Philippines on Sunday night.

Paddock paid for her ticket there and also wired her $100,000 in cash but Danley, 62, believed it was his way of breaking up with her.

She flew back to the US on Wednesday at the request of police after earlier telling family that her conscience was clear.

Detectives appeared convinced on Friday that someone else, somewhere, held information which could solve the mystery of what drove Paddock to commit the killings.

Police have confirmed that Paddock was the only shooter in the Mandalay Bay suite where he carried out the attack and say no one else accessed the room beforehand

'It's really imperative that the listening public have a very clear understanding that there are still a number of people out there that know something looked of place.

'If you know something, you need to say something,' McMahill said.

One suggested motive that was put forward by a reporter on Friday was that Paddock was 'obsessed' with the month of October however McMahill could not give any credit to the suggestion that it is what may have caused the killings.

We have not stopped nor will we stop. We have a long way to go. Las Vegas Metropolitan Police Undersheriff Kevin C. McMahill

He said they were 'keenly' pursuing his medical records to verify reports that he was taking prescription drugs and had potentially deteriorated into mental illness.

At Friday's press conference, detectives also gave further detail about some of the explosives that were found inside Paddock's car which was parked in the hotel parking lot.

It contained 50lbs of tannerite - an exploding target which triggers mass explosions when shot at. It is made out of ammonium nitrate and aluminum powder.

McMahill said he did not know what Paddock planned to do with the material but said it had not been modified in anyway to turn into an IED as was reported.

He also dismissed claims that someone else accessed the room using Paddock's key card while his Hyundai was not in the parking lot.

Detectives are working through 'voluminous' amounts of surveillance footage from inside the hotel, he said, but have so far not been able to find any other suspect.

It was also revealed that hotel security guard Jesus Campos, who alerted police to Paddock's specific location after being shot in the leg when he disturbed his killing spree, was on the floor investigating an open door on one of the rooms.

Along with the dozens of guns and ammunition found inside the room (above), Paddock had 50lbs of the explosives tannerite in his Hyundai in the underground parking lot of the hotel

On Friday, workers were seen repairing the blown out windows in Paddock's suite which he smashed to gain a clear view of the crowd

The suite was on the 32nd floor of the iconic hotel. Paddock blew out two of the windows

McMahill did not say whether it was Paddock's room which triggered the alarm but he offered a clearer picture of how Campos found himself in the firing line.

'Jesus Campos is a true hero. He was dispatched to what they call a door alarm on the 32nd floor,' he said, clarifying that such an alarm was issued when a door was left ajar.

'He went up there to investigate and as he was doing his job diligently, he came under fire from our suspect.

'He was struck in the leg, and he turned around retreated. He notified his dispatch which was absolutely critical to us knowing the location as well as advising the responding officers as they arrived on that 32nd floor.

'This was a remarkable effort by a brave and remarkable man. I don't think we've done a good enough job of recognizing him and his actions. For that I apologize.

'I want to clear the record. He is an absolute hero,' McMahill added.

Marilou Danley, Paddock's 62-year-old girlfriend, is seen returning to the USA at LAX on Wednesday morning

Insiders say Marilou (above with her back to the camera) was often 'jittery' around Paddock

The undersheriff also dismissed, again, the repeated claims from ISIS that Paddock carried out the attack in the name of Islamic terror.

The FBI also announced on Friday the launch of a designated campaign to the public for information.

Police are not yet able to tell the survivors who abandoned their belongings at the concert venue as they fled the scene when they will be able to retrieve them.

'We have thousands of pieces of property left on the field that day. We are diligently looking at ways to catalogue it, collect it and find the mechanism to return it but we're still days away from allowing that to happen,' he said.

The Route 91 Harvest festival was not the first music event Paddock targeted.

Undersheriffs said they are still 'days away' from being able to tell the survivors when they can collect personal items that were left at the scene. Above, piles of organized items including a strollers and wheelchairs are seen lined up into various piles of evidence

Makeshift memorials have been set up across Las Vegas in memory of the victims

In August, he rented hotel rooms overlooking the Lollapalooza festival in Chicago which Malia Obama attended with friends.

Paddock never showed up for the event despite reserving a suite in the hotel.

Police say they 'will not sto' until they determine what Paddock's motive was

A picture is slowly emerging of how he deteriorated into a gambling addiction in recent years, at times blowing $100,000 a time on video poker.

Paddock, whose family said made millions through real estate deals, was considered a low roller but spent enough in the casinos that he frequented to be treated favourably by staff.

His $500-a-night suite at the Mandalay Bay was comped because he always spent so much there.

Such was his relationship with other casinos that his girlfriend Marilou would be given all-expenses paid shopping trips by some of the establishments.

Paddock and Marilou lived in a $400,000 home in a retirement community in Mesquite, Nevada.