The Las Vegas gunman meticulously planned his attack with chilling precision, down to a camera hidden in a food service cart in the hallway

Three days after a gunman unleashed an 11-minute stretch of gunfire upon a crowd of 22,000 concertgoers from his perch on the 32nd floor of a Las Vegas hotel, investigators remain dumbfounded by the lack of clues as to his motive.

Stephen Paddock, a 64-year-old retired accountant, had no prior criminal record, left no social media footprint, and had not established any apparent ties to extremist groups, officials say. His attack was the deadliest mass shooting in modern American history, killing 58 and leaving 527 injured.

But what authorities have made clear so far is that Paddock methodically planned every detail of his attack, ensuring he had a massive arsenal of weapons outfitted to maximize carnage, and a network of cameras set up inside and outside his hotel room, presumably to alert him when law enforcement arrived to take him down.

"I anticipate he was looking for anybody coming to take him into custody," Clark County Sheriff Joseph Lombardo told media Tuesday afternoon. "It was pre-planned, extensively, and I'm pretty sure that he evaluated everything that he did in his actions, which is troublesome."

Paddock checked into his suite at the Mandalay Bay hotel on Thursday, September 28. Over the next few days, he hauled up more than 10 suitcases filled with firearms, though hotel staff said they spotted nothing "nefarious," according to Lombardo.

He kept the "Do Not Disturb" sign on his door throughout his stay so no maids would enter, an anonymous hotel worker told The New York Times.

Paddock amassed his weapons cache over a period of years, purchasing them legally in Nevada, California, Utah, and Texas, officials said. When investigators entered his room, they found 23 guns, including AR-15-style and AK-47-style rifles, and a hammer Paddock had apparently used to smash out two of the hotel suite's windows.

Twelve of the rifles recovered from Paddock's suite had been retrofitted with "bump stock" devices, which enable semi-automatic weapons to achieve rapid-fire capabilities, an agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives told media on Tuesday.

Authorities recovered an additional 24 rifles, shotguns, and pistols from two Nevada properties owned by Paddock. He purchased 33 firearms in the last year alone.

Beyond the weaponry, Paddock appears to have planned out the rampage down to the moment police stormed his suite. He set up an elaborate surveillance system, placing cameras in the hallway outside his suite, on a food-service cart, and over the peephole of his door.

The cameras appear to have been effective - Paddock at one point shot through his suite door and wounded a security guard. Paddock then turned one of his guns on himself, pulling the trigger as SWAT officers closed in around his suite.

Even the absence of Paddock's girlfriend Marilou Danley, who traveled to the Philippines a week before the shooting, appears to be part of his plan, according to her sisters. Danley, whom authorities are questioning as a person of interest, arrived back in the US late on Tuesday night escorted by FBI officials.

"She was sent away so that she will be not there to interfere with what he's planning," one of Danley's sisters told Australia's Channel 7 TV network. The network withheld both sisters' names.

Paddock's brother Eric offered a similar theory.

"He manipulated her to be as far away from here and safe when he committed this," he told The Washington Post. "The people he loved he took care of, and as he was descending into hell he took care of her."