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.