President Donald Trump has described the gunman who killed 59 people and injured 527 in Las Vegas on Sunday as "a sick man, a demented man".
Speaking at the White House, he said he would look at gun laws "as times goes by" but he did not elaborate.
Police are still trying to find out why Stephen Paddock, 64, opened fire on an open-air concert from the 32nd floor of the nearby Mandalay Bay Hotel.
Police found 23 guns in his room and firearms and explosives at his home.
As yet, no clear reason for the killing has emerged and investigators have found no link to international terrorism. Some investigators have suggested Paddock had a history of mental illness, but this has not been confirmed.
Paddock had no criminal record and was not known to police.
Speaking to reporters as he was about to board the presidential helicopter, Mr Trump said Paddock was "a sick man, a demented man. Lot of problems, I guess, and we're looking into him very, very seriously".
When asked, Mr Trump declined to call the attack domestic terrorism.
On the issue of gun control, the president said: "We'll be talking about gun laws as time goes by."
Mr Trump, whose position on gun control has changed over the years, gave no further detail.
What do we know of the gunman?
Stephen Paddock, a former accountant with a big gambling habit, lived in a community of senior citizens in the small town of Mesquite, north-east of Las Vegas.
He reportedly lived with a woman called Marilou Danley, who was out of the country in Japan and did not appear to be involved in the shootings, police said.
Las Vegas Sheriff Joseph Lombardo said that when police officers searched the property after the attack, they found 19 "additional firearms, some explosives and several thousand rounds of ammo, along with some electronic devices we're evaluating at this point".
Suspected gunman Stephen Paddock - undated image
Officers also found ammonium nitrate in Paddock's car - the chemical compound used in fertilisers can be used to make bombs such as that used in the 1995 Oklahoma City attack.
David Famiglietti of the New Frontier Armory told the BBC that Paddock had purchased firearms at his store in North Las Vegas in the spring of this year, meeting all state and federal requirements, including an FBI background check.
However, the shotgun and rifle Paddock bought would not have been "capable of what we've seen and heard in the video without modification", Mr Famiglietti said.
The fast shooting rate audible in recordings of Sunday night's attack indicates that Paddock may have modified his guns with legal accessories to make them fire at speeds approaching those of automatic weapons.
Despite the large cache of weapons found in the killer's home, his brother, Eric, is struggling to accept that he acted in this way. He said he was "in shock, horrified, completely dumbfounded".
So-called Islamic State claimed on Monday to be behind the attack, saying Paddock had converted to Islam some months ago. But the group provided no evidence for this and has made unsubstantiated claims in the past.
The IS claim of responsibility for the Las Vegas attack is very unusual in that the perpetrator's profile does not fit that of supporters or "soldiers" that the group has claimed in the past, writes Mina al-Lami, who monitors jihadist groups for the BBC.
The FBI said it had found "no connection to an international terrorist organisation".
How did the attack unfold?
The final shows of the three-day Route 91 country music festival were in full swing when the gunman struck.
According to police, Paddock had booked into the hotel four days earlier, on 28 September, reportedly using some of Ms Danley's identity documents.
Aside from the 23 guns found in the two-room hotel suite, Sheriff Lombardo said there were 10 suitcases.
Thousands were enjoying a performance by top-billing singer Jason Aldean when the first of several bursts of automatic gunfire rang out, starting at 22:08 local time (05:08 GMT on Monday).
Hundreds of shots were fired over at least 10 minutes.
Concert-goers scrambled for cover, flattening themselves against the ground, rushing for the exits or helping others to escape as Paddock sprayed the site from his high vantage point.