Stephen Paddock shot a security guard before he opened fire on an open-air concert in Las Vegas on October 1 killing 59 people, a senior police official announced.

Paddock shot Jesus Campos in the leg, injuring him at 9.59 p.m. on October 1, CNN quoted Clark County Sheriff Joseph Lombardo as saying on Monday night.

“What we have learned is Campos was encountered by the suspect prior to his shooting to the outside world,” Lombardo said.

At 10.05 p.m, Paddock shot numerous rounds into the crowd at the Route 91 Harvest Festival from his room on the 32nd floor of the Mandalay Bay Resort and Casino. He continued firing for about nine to 11 minutes.

Paddock’s final shots were fired at 10.15 p.m., according to a Lombardo. Authorities do not yet know what made him stop shooting.

By the time officers entered the room, Paddock was dead from a self-inflicted gun shot wound, CNN reported.

Investigators are still piecing together evidence left behind in the hotel room and probing Paddock’s background to determine why the retired accountant committed the worst mass shooting in modern US history.

Lombardo said police have found “no evidence to show that there was a second shooter”.