United States President Donald Trump on Tuesday described the gunman behind the Las Vegas mass shooting as a “sick,” “demented” individual.

“He was a sick man. A demented man, a lot of problems,” Trump told reporters as he left the US capital for Puerto Rico. “We are dealing with a very, very sick individual.”

Stephen Paddock, a 64-year-old gambler and retired accountant, was identified as the shooter who fired on a huge crowd at an outdoor country music concert, killing 59 and injuring over 500.

Investigators are trying to establish a motive for the deadliest mass shooting in modern US history, but so far have been unable to pin down what drove Paddock to shoot into the crowds from a 32nd floor hotel room.

Police recovered an arsenal of 23 guns, including automatic weapons, from his room in the Mandalay Bay Resort and Casino across from the concert venue.

More guns, ammunition and explosives were found during a search of Paddock's home in Mesquite, Nevada.