The Sunday night shooting spree from a 32nd-floor window of the Mandalay Bay hotel, on the Las lass Vegas Strip, killed at least 59 people before the gunman turned a weapon on himself. More than 500 people were injured, some trampled, in the deadliest mass shooting in modern U.S. history.

The gunman, identified as Stephen Paddock, 64, left no immediate hint of his motive for the arsenal of high-powered weaponry he amassed, including 42 guns, or the carnage he inflicted on a crowd of 22,000 attending an outdoor country music festival.

Paddock was not known to have served in the military, to have suffered from a history of mental illness or to have registered any inkling of social disaffection, political discontent or radical views on social media.

"He was a sick man, a demented man," U.S. President Donald Trump told reporters. "Lot of problems, I guess, and we're looking into him very, very seriously, but we're dealing with a very, very sick individual."

Read: Gunman Kills 58, Injures Hundreds in Las Vegas

He declined to answer a question about whether he considered the attack an act of domestic terrorism.

U.S. officials also discounted a claim of responsibility by the Islamic State militant group.

Police said they believed Paddock acted alone.

"We have no idea what his belief system was," Clark County Sheriff Joseph Lombardo told reporters on Monday. "I can't get into the mind of a psychopath."

Although police said they had no other suspects, Lombardo said investigators wanted to talk with Paddock's girlfriend and live-in companion, Marilou Danley, who he said was traveling abroad, possibly in Tokyo.

Lombardo also said detectives were "aware of other individuals" who were involved in the sale of weapons Paddock acquired.

The closest Paddock appeared to have ever come to a brush with the law was for a traffic infraction, authorities said.

As with previous mass shootings that have rocked the United States, the massacre in Las Vegas stirred the ongoing debate about gun ownership, which is protected by the Second Amendment to the Constitution, and about how much that right should be subject to controls.

Democrats reiterated what is generally the party's stance, that legislative action is needed to reduce mass shootings. Republicans argue that restrictions on lawful gun ownership cannot deter criminal behavior.

"We'll be talking about gun laws as time goes by," Trump said.

REUTERS