FBI: Mandalay Bay shooter in Las Vegas who killed 58 was angry about how casinos treated him

A trove of documents recently released by the Federal Bureau of Investigation show that the shooter who killed 58 people at a Las Vegas concert in 2017 was "very upset" about how casinos were treating him.

The documents provide the strongest indication yet of a motive for the deadliest mass shooting in modern American history.

Stephen Paddock, 64, a regular gambler who had a penchant for video poker, killed himself at the Mandalay Bay Resort & Casino before he could be apprehended. The documents provide the most detailed look to date into Paddock's possible motive and gambling habits, delving into the weeks and years before he fired from his 32nd-floor windows into a crowd of 22,000 people at the Route 91 Harvest Festival.

A fellow gambler told the FBI that "Paddock was very upset at the way casinos were treating him and other high rollers," noting that roughly three years earlier casinos had started banning high rollers from certain events, hotels and even casinos.

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The gambler described Paddock as a high roller with a bankroll of approximately $2 million to $3 million who preferred playing video poker. The report states that the acquaintance believed the stress about how high rollers were being treated could "easily be what caused Paddock to 'snap.'"

The Mandalay Bay hotel, Paddock's acquaintance told the FBI, "was not treating Paddock well because a player of his status should have been in a higher floor in a penthouse suite."

The collection of FBI documents were released last week in response to a public records request by The Wall Street Journal.

Who was Stephen Paddock?

Paddock gambled hundreds of thousands of dollars in Las Vegas, Reno and other Nevada properties over roughly a decade prior to the shooting, according to records provided to the FBI by the Nevada Gaming Authority that were among the newly released documents.

In 2006, for example, Paddock gambled more than $945,000 and came out with roughly $4,300 in winnings. During September, the month prior to the Oct. 1, 2017, shooting, Paddock had four reservations at Mandalay Bay Resort & Casino.

Paddock considered himself a professional gambler, according to the documents, and told one person interviewed by the FBI that it had become his main source of income roughly three years prior to the shooting.

"Paddock purchased handgun out of concern that he had been earning a lot of cash and wanted it as a means of protection," the person, whose identity was not disclosed, told the FBI. The individual told the FBI Paddock had mentioned that he was banned from several casinos because he had "made too much money from them."

An FBI Behavioral Analysis Unit brought together a panel of experts for a yearlong look at what motivated Paddock to fire over 1,000 rounds at the crowd over 11 minutes. The panel concluded that there was "no single or clear motivating factor" that drove him to the rampage.

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Another woman interviewed by the FBI at the Tropicana hotel in Las Vegas noted that Paddock would visit once every three months or so, usually during the week to play casino games.

"Paddock only wanted to discuss gambling," she said, recalling that during one stay from Sept. 12 to 14, just a few weeks before the shooting, Paddock lost $38,000.

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'No evidence of a conspiracy'

In 2018, Las Vegas Sheriff Joe Lombardo said that a 10-month investigation by the department resulted in "no evidence of conspiracy or a second gunman" and no definitive motive for the shooter.

Investigators determined that Paddock spent $1.5 million over two years, including debts paid to casinos; meanwhile, a look at 14 of his bank accounts showed he had $2.1 million in September 2015 but only about $530,000 two years later.

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Follow Tami Abdollah on Twitter @latams or email her at tami(at)usatoday.com

This article originally appeared on USA TODAY: FBI: Mandalay Bay shooter who killed 58 angered by how casinos treated him