On Oct. 1, 2017, what was reportedly the worst mass shooting in U.S. history occurred in Las Vegas, Nevada, when an alleged lone gunman, Stephen Paddock, opened fire on thousands of concert-goers from the elevated position of a casino hotel room and murdered 59 people while causing injury to more than 500 others.

Now, nearly six years after the fact, the FBI has released to the public hundreds of heavily redacted documents related to its investigation of the deadly incident, and those documents purportedly suggest that Paddock's anger at how he was treated by multiple casinos could have led him to commit the mass shooting, Fox News reported.

Paddock is alleged to have used multiple rifles to fire thousands of rounds from a room on the 32nd floor of the Mandalay Bay Casino and Resort down toward the tens of thousands of people gathered for the Route 91 Country Music Festival before eventually turning a gun on himself before police officers could breach the hotel room.

FBI appears to blame anger at casinos for mass shooting

Per the FBI documents, Paddock was described as a "prolific video poker player" who made a living solely from gambling and traveled to Las Vegas every few months or so and reportedly had lost roughly $38,000 just a couple of weeks before the shooting.

An unnamed fellow gambler said to have been familiar with Paddock is purported to have told investigators that the alleged gunman "was very upset at the way casinos were treating him and other high rollers," as well as that he was "personally upset and stressed out about the treatment he and other high rollers received in recent years and believed the stress could have easily caused Paddock to 'snap.'"

That anonymous gambler is further purported to have said that Paddock was also angry that the Mandalay Bay Casino had situated him in a room on the 32nd floor because he believe that "a player of his status should have been on a higher floor in a penthouse suite."

For perspective, Fox News noted that "high rollers" in Las Vegas used to receive highly preferential treatment from the casinos in the form of various perks that included complimentary penthouse suites, free cruises and flights, expensive cars, and other gifts to curry favor, but had stopped doing so in recent years and instead had begun to ban or restrict high rollers from certain events, resorts, or casinos.

In fact, the FBI documents, which suggested that Paddock usually had a bankroll of $2-3 million while gambling, had actually been banned from three separate casinos in Reno, Nevada due to the frequency with which he won large sums of money.

Las Vegas police continue to insist that no motive was ever determined

The Associated Press reported that the FBI released the heavily redacted documents in response to a records request filed by The Wall Street Journal.

No definitive motive had ever been ascribed to the 2017 mass shooting, and both the FBI and Las Vegas police had closed their investigations after about a year with only limited information being shared with the general public about what had occurred.

In response to the document dump, a spokesperson for the Las Vegas police said in a statement, "We were unable to determine a motive for the shooter," and noted that "Speculating on a motive causes more harm to the hundreds of people who were victims that night."

Former lead investigator disputes claimed possible motive

A former Las Vegas Metro Police official who led the investigation into the shooting, Kelly McMahill, told the AP that she had seen no indications that Paddock's actions had been motivated by anger or frustration with the casinos, and said, "There’s no way that LVMPD would have hidden any potential motive from our victims and survivors for five years."

"What we know from (Paddock’s internet) search history is that he was looking for a large crowd of people, which, of course, he ended up finding," she continued about prior revelations that Paddock had scouted out other major outdoor concert events as possible targets.

"If we ever discover a motive, whether it’s 10 years from now, 20 years from now, I have faith that LVMPD would contact victims first before making something public," she added. "It’s the right thing to do."