The FBI were questioning Marilou Danley, Paddock's girlfriend, on Wednesday night to see if she could provide any clues - but in a statement Ms Danley said she was "unaware" of any of his actions that led to the shooting.
Mr Trump largely stuck to a talking point repeated by dozens upon dozens of Republican officials: "Well, we're not going to talk about that today".
The two officers arrive on Paddock's floor.
Video poker machines are seen at Green Valley Ranch in Henderson on Wednesday, Sept. 28, 2011.
Marilou Danley broke her silence on Thursday.
Trump's first stop was the University Medical Center, where he met privately with victims of the Sunday night shooting rampage, their families, and medical professionals.
"I will co-operate fully with them".
Former Presidents Barack Obama and Bill Clinton joined other world leaders - including those from the United Kingdom, Canada and Mexico - sharing condolences for victims. "He was a sick man, a demented man", US President Donald Trump said.
Throngs of blood donors lined up for hours to help the wounded.
Friends and family are asked to report missing people believed to be connected to the shooting using the hotline 1-800-536-9488.
The motives of the multimillionaire retired accountant, who was not known to be suffering from mental illness, are unknown.
"It never occurred to me in any way whatsoever that he was planning violence against anyone", she said. "Americans defied death and hatred with love and with courage".
"The genetics load the gun, personality and psychology aim it, and experiences pull the trigger, typically", Clemente said.
Pundits will take to television and argue.
Lombardo's frank comments put into doubt an explanation previously put forward by authorities that he was a "lone wolf".
Officials said Paddock purchased 33 weapons since October 2016 - most of them rifles.
The first shot was fired at 10:05 p.m. Sunday, and ended at 11:27 p.m. when the suspect was confirmed down. As for what triggered the massacre, the brother said: 'Something happened that drove him into the pit of hell'.
He said Stephen Paddock was an avid gambler who had "no history of violence". One camera looked out the peephole on the suite's door. "He escaped and (left) us here putting (pieces of) the puzzles together".
"She's a good person, a gentle soul, a mother, a grandmother, a sister, a friend", the sister said, adding that Danley was having trouble coping with the tragedy because "she's a very weak person". He killed himself as police closed in.
But it gets harder for me to say that, to believe that, each time something like this happens.
Casino regulators are looking closely at Paddock's gambling habits and checking their records to see whether he had any disputes with casinos or fellow patrons.
In the immediate aftermath of the shooting, police described Danley only as a "traveling companion" of the shooter. One photo shows Paddock's legs splayed on the floor near several weapons, apparently after he killed himself.
The nurse said she was far from alone. Don't look for Trump to say that gun restrictions are needed.
In explaining his theory, the sheriff mentioned Paddock's arsenal of 47 guns and a "plethora" of ammunition, plus his two Nevada residences.