"Well, it's a very sad thing," Mr Trump told reporters at the White House as he left for Nevada.
"We're going to pay our respects and to see the police who have done really a fantastic job in a very short time."
The president also said "a lot more" was emerging about the gunman. "That'll be announced at the appropriate time," he added.
From his 32nd-floor suite at the Mandalay Bay Hotel, Paddock, a retired accountant with no criminal record, sprayed bullets into a crowd at a country music festival below. He killed 58 concertgoers and injured more than 500, before apparently killing himself.
Police officials quoted by the Reuters news agency said they hoped Ms Danley - an Australian citizen who moved to the US 20 years ago - would consent to be interviewed voluntarily.
Is Marilou Danley a suspect?
US authorities have named Ms Danley a "person of interest" in their investigation, , and said they made contact with her shortly after the shooting.
She had been in the Philippines since late September, local media reported.
Her sisters told Australian outlet 7News that Ms Danley had not known about the trip until Paddock told her he had bought her a ticket to the Philippines. "She was sent away... so that she will not be there to interfere with what he's planning," they said.
Paddock checked into the Mandalay Bay Hotel on 28 September, reportedly using some of Ms Danley's identity documents.
The Philippines' National Bureau of Investigation told AFP news agency it was investigating reports that Paddock sent $100,000 to Ms Danley in the Philippines days before the shooting.
Ms Danley's sisters also told 7News that she had been wired that amount in the Philippines.
An unnamed US official told Reuters news agency that investigators were assuming the amount was intended as a form of life insurance.
What kind of relationship did the pair have?
Eric Paddock, the youngest brother of Stephen Paddock, told the New York Timesthat his brother loved and doted on Ms Danley.
"She was probably one of the only people I've ever seen that he'd go out of his way to do a little thing for," he said.
But the pair are also said to have had a turbulent relationship, according to other reports. The Los Angeles Times has spoken to people who witnessed Paddock verbally abusing Ms Danley at a coffee shop in Mesquite, Nevada.
The 62-year-old was reportedly born in the Philippines
Lived in Queensland for about 10 years in the 1980s while married to an Australian
She then moved to the US and was married to American Geary Danley, whom she divorced in 2015
Used to work as a casino hostess attending to "high-limit" players, and is thought to have met Stephen Paddock in a Nevada casino
US police say she had been living in Nevada with Paddock
Sources: Australian Broadcasting Corporation, US media outlets
What is the latest in the investigation?
Police say Paddock set up a number of cameras in and around his hotel suite.
Two cameras in the hallway and one in the peephole allowed him to see if "law enforcement or security" were approaching, they said.
Although the authorities are still unable to explain why a 64-year-old gambler and retired accountant should want to carry out a mass shooting by hauling such a vast arsenal of weapons to the hotel, they do know there was a high degree of planning.
The authorities in Las Vegas revised the death toll down from 59 on Tuesday evening, saying that one of the bodies was that of the gunman.
Paddock, who had a big gambling habit, lived in a community of senior citizens in the small town of Mesquite, north-east of Las Vegas.
He reportedly shared his house there with Marilou Danley.
Nineteen firearms, some explosives and several thousand rounds of ammunition with electronic devices were found at the property.
According to reports, Paddock had a troubled upbringing - his father was a bank robber who regularly beat him and his three brothers, while his mother struggled to cope bringing up the family.
A contrasting picture of the gunman has emerged - with some describing him as cold and stand-offish and others saying he was friendly. One of his three brothers told US media that he gave financial support to his elderly mother.
Will the attack trigger more demand for gun controls?
The shooting has prompted calls for reform to US gun laws.
But Mr Trump - who has been backed by the National Rifle Association, and spoke often of protecting gun rights during his campaign - has tried to steer clear of leaning too far either way.
After visiting Puerto Rico on Tuesday, he said "perhaps that [time] will come" for a debate.