LAS VEGAS — The Las Vegas gunman planned his massacre so meticulously that he even set up cameras inside his high-rise hotel room and on a service cart outside his door, apparently to spot anyone coming for him, the sheriff said Tuesday.
Meanwhile, Sheriff Joseph Lombardo named the gunman's girlfriend as a "person of interest" and said the FBI is bringing her back to the U.S. for questioning as investigators try to determine why Stephen Paddock killed 59 people in the deadliest mass shooting in modern U.S. history.
Investigators have been speaking with Marilou Danley, who is traveling in the Philippines, and "we anticipate some information from her shortly," Lombardo said.
Lombardo said he is "absolutely" confident authorities will find out what set off Paddock, a 64-year-old high-stakes gambler and retired accountant who killed himself before police stormed his 32nd-floor room.
The cameras Paddock set up at the Mandalay Bay hotel casino were part of the extensive preparations that included stockpiling nearly two dozen guns before opening fire from his perch on the closing night of a three-day country music festival below.
"I anticipate he was looking for anybody coming to take him into custody," Lombardo said.
During the Sunday night rampage, a hotel security guard who approached the room was shot through the door and wounded in the leg.
"The fact that he had the type of weaponry and amount of weaponry in that room, it was preplanned extensively," the sheriff said, "and I'm pretty sure he evaluated everything that he did and his actions, which is troublesome."
Lombardo said the investigation is proceeding cautiously in case criminal charges are warranted against someone else.
"This investigation is not ended with the demise of Mr. Paddock," the sheriff said. "Did this person get radicalized unbeknownst to us? And we want to identify that source."
In addition to the cameras, investigators found a computer and 23 guns with him at the hotel, along with "bump stock" devices that can enable a rifle to fire continuously, like an automatic weapon, authorities said. Nineteen more guns were found at Paddock's Mesquite home and seven at his Reno house.
Video shot outside the broken door of the room show an assault-style rifle with a scope on a bipod. The sheriff said an internal investigation has been launched to find out how that footage was obtained.
Some investigators turned their focus Tuesday from the shooter's perch to the festival grounds where his victims fell.
A dozen investigators, most in FBI jackets and all wearing blue booties to avoid contaminating the scene, documented evidence at the site where gunfire rained down and country music gave way to screams of pain and terror.
"Shoes, baby strollers, chairs, sunglasses, purses. The whole field was just littered with things," said Nevada Attorney General Adam Laxalt, who told The Associated Press it was like a "war zone." ''There were bloodstains everywhere."
More than 500 people were injured in the rampage, some by gunfire, some during the chaotic escape. At least 45 patients at two hospitals remained in critical condition. All but three of the dead had been identified by Tuesday afternoon, Lombardo said.
As for what may have set Paddock off, retired FBI profiler Jim Clemente speculated that there was "some sort of major trigger in his life — a great loss, a breakup, or maybe he just found out he has a terminal disease."
Clemente said a "psychological autopsy" may be necessary to try to establish the motive for the attack. If the suicide didn't destroy Paddock's brain, experts may even find a neurological disorder or malformation, he said.
He said there could even be a genetic component to the slaughter: Paddock's father was a bank robber who was on the FBI's most-wanted list in the 1960s and was diagnosed a psychopath.
"The genetics load the gun, personality and psychology aim it, and experiences pull the trigger, typically," Clemente said.
Paddock had a business degree from Cal State Northridge. In the 1970s and '80s, he worked as a mail carrier and an IRS agent and held down in an auditing division of the Defense Department, according to the government. He later worked for a defense contractor.
He had no known criminal record, and public records showed no signs of financial troubles, though he was said to be a big gambler.
Nevada's Gaming Control Board said it will pass along records compiled on Paddock and his girlfriend to investigators.
"No affiliation, no religion, no politics. He never cared about any of that stuff," his brother, Eric Paddock, said outside his Florida home. He said he was at a loss to explain the massacre.
The FBI discounted the possibility of international terrorism early on, even after the Islamic State claimed responsibility for the attack.