LAS VEGAS — Before he mowed down concertgoers from a perch high in a hotel tower, Stephen C. Paddock created a ring of surveillance around him, with video cameras in his suite and in the hallway, law enforcement officials said on Tuesday. But investigators were still at a loss to offer a motive for the massacre.

The cameras — apparently intended to warn of approaching threats — along with the 23 guns, hundreds of rounds of ammunition, and other equipment found in the gunman’s hotel suite, suggested a thought-out plan to have plenty of time to wreak carnage while holding the police at bay.

Local and federal investigators were also eager to interview the gunman’s girlfriend, Marilou Danley, who had been in the Philippines. She arrived at Los Angeles International Airport on Tuesday night and was met by the authorities, according to a law enforcement official. Sheriff Joseph Lombardo of the Las Vegas Metropolitan Police Department said that at a minimum, she might shed some light on what was going through the mind of the gunman, who killed himself as the police prepared to enter his room.

Twelve of the rifles Mr. Paddock had in his luxury suite on the 32nd floor of the Mandalay Bay Resort and Casino were outfitted with a “bump stock,” a device that enables a gun to fire hundreds of rounds per minute, like a machine gun, which may explain how he was able to rain such devastation on the crowd below, law enforcement officials said. Such devices are generally legal, and the possibility that he may have used them set off a fresh round of calls by Democratic lawmakers in Washington to pass more gun regulations after the tragedy.

At 10:07 p.m. on Sunday, the gunman opened fire on the thousands of people attending a country music festival a few hundred yards northeast of the hotel, firing long, rapid-fire bursts as people screamed and ran for their lives. He killed 59 people — the coroner clarified on Tuesday that the number included Mr. Paddock, along with his 58 victims — and wounded hundreds of others. In all, more than 500 people were injured, most by gunfire, and some in the panicked rush to escape.

President Trump, who is expected to visit Las Vegas on Wednesday, said on Tuesday that Mr. Paddock was “a sick man, a demented man,” adding that “we are dealing with a very, very sick individual.” He said there would be some discussion about firearms legislation, but was not specific.

“We will be talking about gun laws as time goes by,” Mr. Trump said as he prepared to leave Washington for hurricane-battered Puerto Rico.

Police officials said that Mr. Paddock, 64, had set up two cameras in the hallway, including one on a service cart, and a third camera over the suite door peephole.