The man who killed 58 people in the worst mass shooting in modern US history is seen in newly released CCTV footage calmly chatting with other people and taking suitcases hiding ammunition to his room just before carrying out the murders.

Stephen Paddock gambles and nonchalantly talks to other guests and staff at the Las Vegas hotel where he was staying.

He betrays no clues to planning a massacre, although records show that over several days Paddock amassed an arsenal of 23 assault-style rifles and a handgun in his suite.

Within days of the footage being taken last September, he would use the arsenal he had brought in inside suitcases to fire indiscriminately, shooting dead 58 people and wounding more than 500 others at an outdoor concert, as he targeted them from the window of his suite at the Mandalay Bay Resort and Casino.

The footage provided by MGM Resorts International also shows Paddock wheeling suitcases to lifts, gambling at high-limit video poker, buying snacks and driving into the valet area.

Paddock was filmed repeatedly leaving the hotel for his home in Mesquite, returning with a minivan loaded with suitcases. The valets take his keys; concierges stack his luggage on gold trolleys, helping him transport at least 21 bags upstairs over several days. Paddock chats and jokes with them.

“Paddock gave no indication of what he planned to do and his interactions with staff and overall behaviour were all normal,” company spokeswoman Debra DeShong said in a statement.

stephen-paddock.jpg, by Jane Dalton (AP)

“MGM and Mandalay Bay could not reasonably foresee that a long-time guest with no known history of threats or violence and behaving in a manner that appeared outwardly normal, would carry out such an inexplicably evil, violent and deadly act,” she said.

Paddock, 64, a retired accountant who amassed a millionaire's fortune, died of a self-inflicted gunshot to the head.