Stephen Paddock spent three days at the hotel before carrying out the horrifying attack, killing 59 people and injuring 527 in a shooting spree during a Route 91 music concert in Las Vegas.
He used a stash of 23 weapons to fire down a barrage of bullets from room 135 on the 32nd floor of the hotel.
A former Las Vegas Metropolitan Police Department officer said Stephen Paddock had been staying at the Mandalay Bay hotel-casino for three days before the shooting took place.
Randy Sutton, who spent 24 years with the police force, told CBS This Morning the amount of firepower in the room indicated it was not all brought up in just one trip.
Mr Sutton said: “He certainly didn’t have bellmen bring that up.
“So having been there for three days, he had the time to bring that up probably in either luggage or a golf bag or something of that nature.”
Police also revealed that Paddock fired special ‘incendiary’ bullets at a jet fuel tank, probably in the hopes of causing a massive explosion. Authorities had said earlier that he fired two conventional rounds at the tank, but failed to penetrate it.
The rounds, meant to ignite what they hit, were found inside Paddock’s room at the Mandalay Bay Resort and Casino and near the fuel tank a short distance away on the grounds of McCarran International Airport.
Despite the ongoing investigation the US authorities are no nearer to establishing a motive for Paddock’s actions.
Sheriff Joseph Lombardo told a news conference: “I can’t get into the mind of a psychopath.”
Most of those found in the hotel room are military-style rifles, while two were modified with a “bump stock” device.
Authorities are investigating whether those items were used to modify weapons used in the massacre.
This device allows the shooter to fire off rounds quickly without converting it to a fully automatic weapon.
A semiautomatic weapon requires one trigger pull for each round fired while a fully automatic weapon requires just one trigger pull to unleash continuous rounds until the magazine is empty.
Police have not yet confirmed the weapon Mr Paddock used in the massacre, but said he smashed the hotel windows with a hammer-like object to get a clear shot at the 22,000-strong crowd.
Separately, a maintenance worker said he told hotel dispatchers to call police and report a gunman had opened fire with a rifle inside Mandalay Bay before the shooter began firing.
Stephen Schuck told NBC News that he was checking out a report of a jammed fire door on the 32nd floor of Mandalay Bay when he heard gunshots and a hotel security guard, who had been shot in the leg, peaked out from an alcove and told him to take cover.
Mr Schuck said: “As soon as I started to go to a door to my left the rounds started coming down the hallway.
“I could feel them pass right behind my head.
“It was kind of relentless so I called over the radio what was going on. As soon as the shooting stopped we made our way down the hallway and took cover again and then the shooting started again.”