The gunman who killed 58 people and injured over 500 at a Las Vegas concert last month had lost a significant amount of money in the past two years. Police think that might be a "determining factor" in the worst mass shooting in modern US history.

Stephen Paddock was a high-stakes gambler and real estate investor who had lost a “significant amount of wealth” since September 2015, which led to “bouts of depression,” Clark County Sheriff Joe Lombardo said in an interview with news station KLAS-TV.

“This individual was status-driven, based on how he liked to be recognized in the casino environment and how he liked to be recognized by his friends and family,” Lombardo said. “So, obviously, that was starting to decline in the short period of time, and that may have had a determining effect on why he did what he did.”

Las Vegas shooter was on a losing streak in the two years before the massacre, leaving him depressed, sheriff says. https://t.co/8hYtJEIH3z — AP West Region (@APWestRegion) November 3, 2017

Lombardo said investigators haven’t uncovered exactly what led Paddock to unleash a barrage of gunfire into a crowd of concertgoers from his high-rise hotel suite.

“We are doing an autopsy on his brain, the coroner is in the process of having that completed. Which takes some time,” Lombardo said. “We don’t know if he had a mental defeat which caused him to change.”

“I hope we find something in his brain,” he added.

Investigators still consider Paddock’s girlfriend Mary Lou Danley a person of interest, who is still being actively interviewed. Lombardo said that, while investigators thought her account was accurate, they questioned her about Paddock’s purchase of 40-50 guns in a short period of time.

“It is hard for me to believe,” said Lombardo. “You would think Ms. Danley would have some information associated with that.”

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There had to be a trigger point to cause Paddock to start purchasing large amounts of weapons in a short period of time, but “we have yet to determine what it is,” the sheriff said.

“Obviously he took a long time to think this out, process, obtained the weaponry, the logistics, thought out the plan, so it may be a longer term issue that made him snap,” said Lombardo. “We may not find out.”

One of the laptops found in Paddock’s hotel suite was missing a hard drive, and searches of his internet history turned up nothing unusual. Investigator found no evidence that Paddock had help in carrying out the attack.

Lombardo dismissed speculation that he acting like a sniper or had knowledge of weapons, describing him as “a psychotic individual in possession of a firearm shooting into a crowd.”

“It wasn’t difficult to do what he did,” the sheriff said. “I don’t want to say he was a genius. It was diabolical.”

As for Paddock taking his own life, Lombardo said “I believe the suspect believed the wolf was at the door.”

Several news organizations have sued for 911 calls, police video and search warrants related to the shooting.