THE sheriff leading the investigation into the Las Vegas shooting believes the gunman was not acting alone and that he most likely had an accomplice.

Speaking to reporters on Wednesday afternoon, sheriff Joseph Lombardo said "he had to have some help".

Mr Lombardo said investigators did not have any other suspects at this stage, but they were "determined to find out if there was".

"You look at the weapon obtaining, the different amounts of Tannerite [explosives] available, do you think this was all accomplished on his own?

"On face value, you've got to make the assumption he had to have some help at some point, and we want to ensure that that's the answer."

Mr Lombardo's frank comments put into doubt explanation previously put forward by authorities that he was a "lone wolf".

In explaining his theory, the sheriff mentioned Mr Paddock's arsenal of 47 guns and a "plethora" of ammunition, plus he's two Nevada residences. He also made mention of his girlfriend, former Australian resident Marilou Danley, who has been named as a "person of interest" in the investigation.

"Maybe he's a super guy that was working this all out on his own, but it would be hard for me to believe that," the sheriff said.

"Here's the reason why: Put two and two together. Another residence in Reno with several firearms, electronics and everything else associated with large amounts of ammo, a place in Mesquite, we know that he had a girlfriend. Do you think this is all self-facing? An individual, without talking to somebody, just sequestered among themselves? I mean, come on folks."

Federal Bureau of Investigation special agent in charge Aaron Rouse confirmed that Ms Danley had been interviewed after she flew into Los Angeles from the Philippines Tuesday overnight, but she is not in police custody.

He also said that investigators had no evidence to indicate Paddock's attack was linked to international terrorism.

PADDOCK GAMBLED BEFORE DEADLY ATTACK

In the hours before he opened fire on the Route 91 Harvest Festival, Paddock engaged in his favourite pastime: gambling.

"We did see that he was gambling, but we did not see another individual," Mr Lombardo said, without revealing how soon before the massacre his punting took place.

KEY DATE THAT COULD HAVE SET PADDOCK OFF

Police are investigating whether a "mental issue" in October 2016 may have turned Paddock towards violence.

Officials with the Bureau of Alcohol, Tobacco and Firearms confirmed on Wednesday that Paddock had bought 33 firearms, most of them rifles, in the 12 months since October 2016.

Asked whether a "mental issue" or some other incident in a year ago may have compelled him to start his stockpile of weapons, Mr Lombardo said "yes, we are looking into that".

PADDOCK SHOT 200 ROUNDS DOWN HALLWAY

Police have also given new detail about the timeline of the Paddock's shooting massacre.

The sheriff said the gunfire began at 10.05pm Sunday night, a few minutes earlier than initially believed. The first 911 call was received at 10.08pm, and it took police 75 minutes to enter Paddock's hotel room in Mandalay Bay.

A security guard was the first person to discover his location on the 32nd floor, and Mr Lombardo said Paddock released "well over 200 rounds striaght up the hallway". The security guard was hit in the volley of bullets.

The sheriff also indicated that the killer had a plan to escape after his shooting rampage, but he would not be drawn on the details.

News Corp Australia

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