The site of the Route 91 music festival mass shooting is seen outside the Mandalay Bay Resort and Casino in Las Vegas.
LAS VEGAS - The Las Vegas gunman opened fire on a security guard six minutes before he rained down bullets on a crowd and killed 58 people, officials said on Monday in a change to the timeline of the deadliest mass shooting in modern US history.
The shooter, Stephen Paddock, 64, was seen on numerous occasions in Las Vegas alone and he gambled the night before the shooting, Clark County Sheriff Joseph Lombardo said at a news conference.
"This individual purposely hid his actions leading up to this event, and it is difficult for us to find the answers," said Lombardo, who said he was frustrated with the speed of the investigation.
Paddock sprayed an outdoor concert with bursts of gunfire from a Las Vegas hotel window on 1 October, killing 58 and wounding hundreds more, before shooting himself.
"In coordination with the FBI’s behavioural analysis unit, a comprehensive picture is being drawn as to the suspect's mental state and currently we do not believe there is one particular event in the suspect's life for us to [concentrate] on," Lombardo said.
There is no indication anyone other than Paddock fired on the crowd, Lombardo said, adding investigators were talking to family and the girlfriend of the gunman.
BREAKING: Las Vegas sheriff says Paddock shot the security guard 6 minutes before he fired on the concert. pic.twitter.com/PpGrM1SOuZ— Based Monitored ---- (@BasedMonitored) October 9, 2017
Paddock shot and wounded a security guard who came to his floor at the Mandalay Bay hotel to investigate an open door near Paddock's suite, Lombardo said, providing new details on what occurred immediately before the mass shooting.
The security guard, Jesus Campos, was struck in the leg as Paddock, from behind his door, shot into the hallway on the 32nd floor. He apparently detected Campos via surveillance cameras he set up outside his hotel suite, police have said.
Paddock shot the guard at 9.59pm local time, shortly before raining bullets down on the Route 91 Harvest festival in a 10-minute attack that began at 10.05pm.
Police officers found Campos when they arrived on the 32nd floor.
A document in the room contained numbers, Lombardo said, adding he could not immediately say what purpose the figures served.
Las Vegas police officer David Newton told CBS News programme "60 Minutes" on Sunday that he had seen a note on the shooter's nightstand with numbers that appeared to be designed to help his aim.
Lombardo said It was unclear why Paddock had stopped firing at the crowd, suggesting he might have initially planned to escape.
He shot at jet fuel tanks at McCarran International Airport and had protective gear in the hotel suite and explosives in his parked car, Lombardo said.