The gunman responsible for the deadliest mass shooting in modern US history meticulously planned the event and spent decades acquiring weapons, while he lived a secret life, Las Vegas police say.

Police also told a news conference today that 317 of the 489 people injured in the Las Vegas shooting had been discharged from hospitals and the death toll of 59, including gunman Stephen Paddock, remained the same.

Sheriff Joseph Lombardo said Paddock, 64, had 1600 rounds of ammunition and several containers of an explosive commonly used in target shooting that totalled about 22kg in his car.

He said none of the cameras he put up in the hotel room where he unleashed gunfire onto a concert crowd across the Las Vegas Strip on Sunday night were recording.

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Police admit they are still trying to find any reasons why Paddock committed the atrocity.

Police say Las Vegas gunman Stephen Paddock lived a mysterious last 10 years. Photo / AP
Police say Las Vegas gunman Stephen Paddock lived a mysterious last 10 years. Photo / AP

They say Paddock lived a mysterious last 10 years and did not have a lot of personal relationships, the Las Vegas Review Journal's Rachel Crosby reports.

Police say they found found tannerite - a patented exploding target used for firearms practice - and 1600 rounds of ammunition in Paddock's car at the Mandalay Bay. Well over 200 rounds of ammunition were found the hallway.

Las Vegas Metroplitan Police Sheriff Joseph Lombardo confirmed Paddock rented a room at The Ogden through AirBnB during Life is Beautiful, headlined by Kiwi songstress Lorde. It's still unclear why, he said.

Lombardo told a press conference "anything that would indicate this individual's trigger point and that would cause him to do such harm, we haven't understood it yet".

"Usually there is a tell tale sign associated with these type of actions ... We have not found that yet."

He confirmed it was a well-planned attack.

Mourners attend a candlelight vigil in Las Vegas. Photo / AP
Mourners attend a candlelight vigil in Las Vegas. Photo / AP

"This is well thought out. Don't you think the concealment of his history or his life was well thought out?"

He said it was "troublesome that this individual was able to move this amount of gear into a hotel room unassisted."

"Relationship-wise, it is very hard to determine what has occurred in his life in the last decade or so," he added.

The FBI's Aaron Rouse said they were aware Paddock was gambling before the shooting."When we did see he was gambling, we did not see another individual appearing there."

They added that "you've got to make the assumption that he had to have some help at some point."

They said "we haven't been able to determine if there has been anybody else in the room besides him."

They were investigating multiple leads across the United States and the world but said
"we cannot give in to conjecture and we cannot respond to every little Twitter feed that may indicate a theory".

Las Vegas police and emergency vehicles sit on scene following the deadly shooting. Photo / AP
Las Vegas police and emergency vehicles sit on scene following the deadly shooting. Photo / AP

He said there was "no evidence to this point to indicate terrorism".

The girlfriend of the Las Vegas shooter said Wednesday that she had no idea he was planning an attack on the Strip and is devastated for the victims.

A lawyer for Marilou Danley read a statement from her after she was questioned by FBI agents in Los Angeles about her boyfriend, Stephen Paddock. Danley was out of the country at the time of Sunday's attacks and said Paddock sent her to see her family in her native Philippines.

FBI Deputy Director Andrew McCabe, speaking at a cybersecurity forum Wednesday in Boston, said investigators are busy "reconstructing the life, the behavior, the pattern of activity of this individual and anyone and everyone who may have crossed his path in the days and the weeks leading up to this horrific event."

A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip. Photo / AP
A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip. Photo / AP

Asked if investigators had determined why Paddock carried out the attack, he said "we are not there yet."

The FBI has deployed more than 100 individuals from across the country to Las Vegas.

President Donald Trump travelled to Las Vegas to meet with law enforcement officers and survivors of the shooting.