The clues hotel staff may have missed in the days before the Las Vegas shooting.

As investigators work around the clock to try and determine exactly what drove a 64-year-old lone wolf, and retired accountant, to shoot dead 59 people in Las Vegas at the weekend, details of Stephen Paddock’s last days are beginning to come to light.

Las Vegas law enforcement said while they are yet to uncover a motive for the deadliest mass shooting in American history, Paddock’s actions appear to be meticulously pre-meditated.

“It was preplanned, extensively, and I’m pretty sure that he evaluated everything that he did in his actions, which is troublesome,” Clark County Sheriff Joe Lombardo said, according to The Washington Post.

According to a security source who spoke to Fairfax, in the days before the shooting, Paddock asked to be upgraded to an adjoining room with a “better view” in the Mandalay Bay hotel. The room, located on the 32nd floor, housed 23 guns he used to shoot at hundreds of innocent concert-goers who partied on the ground below.

Mia Freedman and Amelia Lester discuss the shooting at Las Vegas’ Mandalay Bay Hotel that left 59 people dead. (Post continues after audio.)

The source refuted Lombardo claims that house-keeping had entered the room sometime between Thursday and Sunday to find nothing amiss, telling the news outlet Paddock had a “do not disturb” sign on the door for three days. In those three days, the source said, no one entered the room.

In that period, Las Vegas Metropolitan Police said Paddock set up a camera in the hotel door’s peephole and had two more cameras set up in the hallway outside his room. One was positioned on a room service cart, and all were set up to allow the gunman to watch for officers who may be approaching the room.

Fairfax also reports CCTV showed Paddock visiting the Mandalay Bay three times recently, fueling speculation he had scrupulously planned the mass murder down to the most minute of details.

Authorities confirmed the 64-year-old transferred $100,000 overseas in the days before the attack. At the time of the shooting, his 62-year-old girlfriend Marilou Danley was in the Philippines.

In an interview with The Washington Post, the gunman's brother said he did not believe Danley had any prior knowledge of the massacre.

“He manipulated her to be as far away from here and safe when he committed this,” Eric Paddock said. “The people he loved he took care of, and as he was descending into hell he took care of her.”

Danley returned to the United States from the Philippines on Tuesday night and was met at the airport by FBI officials.

On Wednesday, lawyer Matthew Lombard delivered a statement from the 62-year-old after she spent several hours being interviewed by FBI agents.