Las Vegas concert-goers who witnessed America's deadliest shooting are being asked to send in photos and videos of the massacre.

US authorities are trying to figure out what motivated Stephen Paddock to shoot into a music festival crowd from a hotel window - killing 59 people before himself.

Around 16 weapons were found in the gunman's hotel room.

1News US correspondent Rebecca Wright told Andrew Dickens FBI agents are investigating how Paddock set up his one-man militia.

"Several of the gun shop owners who sold these guns to Stephen Paddock. Say that he bought those weapons legally, although it's though this morning that he had modified them to make them more deadly."

Wright said US authorities are tying to figure out how he got hold of so many weapons.

"So they will be reviewing CCTV footage. Going through days of footage actually at that hotel, he checked in last Thursday." 

LISTEN ABOVE AS REBECCA WRIGHT SPEAKS WITH LARRY WILLIAMS