LAS VEGAS — Investigators struggled Tuesday with a chilling but baffling array of clues in the wake of the deadliest mass shooting in modern American history as they sought to determine the chain of events that caused a 64-year-old to gun down concertgoers from his hotel suite overlooking the Las Vegas Strip.

“I can’t get into the mind of a psychopath,” said Joseph Lombardo, the sheriff of the Las Vegas Metropolitan Police Department, on Monday.

At the same time, the probes stretched from a ranch-style home near the Arizona border to the 32nd-floor hotel suite used by Stephen Paddock as a place to scan the crowds at a country music festival and then open fire — leaving at least 59 people dead and hundreds more injured in the rain of bullets or trampled in the panicked rush for cover late Sunday. He then killed himself as SWAT officers closed in.

Once again, a stunned nation was left to grapple with a city riven by tragedy and a resurgent debate over gun control and gun violence. The White House and many Republicans said it was a time to mourn rather than launch into political battles, while some Democrats renewed calls for gun safety legislation.

Lombardo warned that the number of dead in Las Vegas could rise, as an additional 527 were thought to have been injured. Hospitals across the region continued to treat patients from the scene, many of them seriously injured. Sunrise Hospital and Medical Center said that as of Tuesday morning, it had 68 patients from the rampage, 33 of them in critical condition.

While the nation learned more about the lives cut brutally short as well as the heroic actions of people on the ground, few answers were available as to what, if anything, may have motivated the rampage.

Authorities described a level of preparation that suggested the massacre was planned in advance. Police said Paddock arrived on Thursday, three days before the shooting, at the Mandalay Bay Resort and Casino on the southern end of the Las Vegas Strip. He took more than 10 suitcases into his suite, officials said.

Paddock aroused no suspicion from hotel staff even as he brought in 23 guns, some of them with scopes. One of the weapons he apparently used in the attack was an AK-47 type rifle, with a stand used to steady it for firing, people familiar with the case said.

Officials recovered another 19 guns as well as thousands of rounds of ammunition and the chemical tannerite, an explosive, at Paddock’s home in Mesquite, Nevada. They also found ammonium nitrate, a chemical that can be used in bomb making, in Paddock’s vehicle, Lombardo said.

Paddock apparently used remote video cameras linked to a tablet in order to keep an eye out for police storming his hotel room, according to two people close to the investigation, who asked not to be identified discussing the ongoing probe.

The idea was apparently to be able to have a security perimeter behind him while he fired down on the crowd — another indication of the planning and forethought Paddock put into the attack. Such a setup would have made it easier for Paddock to know when he was close to being captured.

When police breached his hotel room door and stormed inside, they found him already dead, with blood spread out behind him, mixed in with the empty shell casings on the carpet. He had apparently pointed a silver, black-handled revolver into his mouth and pulled the trigger.

Before that, police and hotel security had scoured several floors of the hotel looking for the shooter and came upon Paddock’s suite, Lombardo said. At some point, Paddock fired through the door and hit a security guard in the leg, he said, adding that the guard is expected to survive.

Paddock had purchased weapons legally over a period of years, from local stores near his homes and from major retailers, like Cabela’s, according to law enforcement officials.

Guns & Guitars, a store in Mesquite, Nevada, said in a statement that Paddock purchased some of his weapons there, but employees followed all procedures required by law, and Paddock “never gave any indication or reason to believe he was unstable or unfit at any time.” Lombardo said Paddock also seemed to have purchased guns in Arizona.

Investigators believe at least one of Paddock’s guns functioned as if it were fully automatic, and they are now trying to determine if he modified it or other weapons to be capable of spitting out a high volume of fire just by holding down the trigger, people familiar with the case said.

Authorities said a sweep of law enforcement databases showed that before the rampage, Paddock had no known run-ins with police. He was the son of a bank robber who was once on the FBI’s most-wanted list, but investigators turned up no clear links to any criminal enterprises or international terrorist groups — despite repeated claims by the Islamic State that Paddock carried out the carnage in its name.

Police said they believe Paddock was a “lone wolf” attacker, though they were still interested in speaking more with a woman named Marilou Danley who lived with him in Mesquite, Nevada, a little more than an hour outside of Las Vegas on the Arizona border.

Danley, Paddock’s 62-year-old girlfriend, was found outside the country – as of Monday afternoon, in Tokyo – and was not involved in the shooting.

“We still consider her a person of interest,” Lombardo said Monday. He said investigators also are exploring a report that Paddock attended a different music festival in September.

People close to the investigation said that in the weeks before the attack, Paddock transferred a large amount of money — something close to $100,000 — to someone in the Philippines, possibly his girlfriend.

The rampage Sunday targeted the Route 91 Harvest festival, a three-day country music concert with grounds across the street from the Mandalay Bay Resort. When the gunfire began Sunday at about 10:08 p.m., some 22,000 people were there, according to police. Country star Jason Aldean was playing what was expected to be one of the last sets of the night as Paddock opened fire, his bullets flying from a window on the casino’s golden facade, which Paddock had smashed with some type of hammer.

“People were getting shot at while we were running, and people were on the ground bleeding, crying and screaming. We just had to keep going,” said Dinora Merino, 28, a dealer at the Ellis Island casino who was at the concert with a friend. “There are tents out there and there’s no place to hide. It’s just an open field.”

The dead included a behavioral therapist who was soon to be married, a nursing assistant from Southern California, a commercial fisherman and an off-duty Las Vegas city police officer. Two other officers who were on duty were injured, police said; one was in stable condition after surgery, and the other sustained minor injuries. Another off-duty officer with the Bakersfield Police Department in Southern California also had injuries that were not life-threatening, according to a statement from the department.

Syed Saquib, a surgeon on duty Sunday night at University Medical Center, said the hospital treated 104 patients, most of whom had gunshot wounds.

“Those that could be saved, were saved,” Saquib said. “There were a few that came in with devastating, non-survivable injuries.”

John Soqui drove seven hours from Arizona to see his 29-year-old niece, who had been shot in the head. Jovanna Martinez-Calzadillas, from suburban Phoenix, had been attending the concert with her husband, a military police officer, Soqui said. Her husband, who was not injured, carried Martinez-Calzadillas away from the concert after she had been shot, relatives said.

“There is just so much hate in this world, and she is my little niece, and I just want to get the guy who shot her,” said Soqui, 51.

Soqui then remembered that Paddock had apparently taken his own life before police stormed into his hotel room. “I want to die, kill myself, just so I can get him,” Soqui added. “So many people have been affected by this, and it’s just killing me that there are people like that out there.”

President Trump ordered flags flown at half-staff and said he would visit Las Vegas on Wednesday.

Leaving the White House to visit hurricane-ravaged Puerto Rico on Tuesday morning, Trump repeated his praise for police in Las Vegas and their response, saying of law enforcement that “what happened in Las Vegas is in many ways a miracle.” He also said that “we’ll be talking about gun laws as time goes by.”

Eric Paddock, Stephen Paddock’s brother, said he was stunned to learn that his brother could be responsible for such violence.

Stephen Paddock had no history of mental illness nor did he have problems with drugs or alcohol, Eric Paddock said, noting that his brother was a high-stakes gambler, sometimes wagering hundreds of dollars on a single hand of video poker.

When he spoke to the FBI, Eric Paddock said he showed agents three years of text messages from his brother, including one that mentioned winning $250,000 at a casino. A federal law enforcement official said investigators had reviewed reports suggesting Paddock engaged in high-dollar gambling, and they are trying to determine whether he faced financial strains.

Eric Paddock said his brother was “wealthy,” in part because he had no children to support. Stephen Paddock had worked in the past as an accountant, and he had real estate investments in the Orlando area, Eric Paddock said. Lockheed Martin, the defense giant, said that Paddock had worked for the company for three years in the 1980s.

Not long after the shooting in Las Vegas, the Islamic State claimed responsibility, though law enforcement authorities were quick to reject that assertion.

“We have determined, to this point, no connection with an international terrorist group,” Aaron Rouse, the special agent in charge of the FBI in Las Vegas, said at a news briefing.

Mark Berman, Devlin Barrett and Matt Zapotosky reported from Washington. Lynh Bui, Felicia Mello and Heather Long in Las Vegas; Barbara Liston in Orlando; Justin Glawe in Mesquite, Texas; and Brian Murphy, Wesley Lowery and Julie Tate in Washington contributed to this report.