In a dramatic shift to the original Las Vegas shooting narrative, over a week after Stephen Paddock rained down bullets on a crowd and killed 58 people, late on Monday Clark County Sheriff Joe Lombardo drastically changed the timeline of the deadliest mass shooting in modern U.S. history, and now the gunman allegedly opened fire on a security guard six minutes before he unleashed the massacre. Officials had previously claimed that Paddock, 64, shot Mandalay Bay security guard Jesus Campos only after Paddock had started shooting at the Route 91 Harvest country-music festival from his 32nd-floor hotel suite on Oct. 1.

The revision to the story also undermines the story surrounding the end of the shooting: officials had previously credited Campos, who was shot in the leg, with stopping the 10-minute assault by turning the gunman's attention to the hotel hallway, where Campos was checking an alert for an open door in another guest's room. However, with the revelation that Campos was shot before his mass shooting, officials now admit they don’t know why he stopped his attack.

Las Vegas Metro PD: Suspect shot security guard before shooting at crowd https://t.co/befniwHBH8 https://t.co/GHSxEOfAtZ — NBC News (@NBCNews) October 9, 2017

As part of the new "story", officials said that police officers who rushed to the hotel room when the shooting began didn't know a hotel security guard had been shot "until they met him in the hallway after exiting the elevator," Lombardo said.

The security guard, Jesus Campos, was struck in the leg as the gunman, from behind his door, shot into the hallway on the 32nd floor. Paddock apparently detected Campos via surveillance cameras he set up outside his hotel suite, police have said.

Paddock shot the guard at 9:59 p.m. local time, Lombardo said, shortly before raining down bullets on the Route 91 Harvest festival in an attack that began at 10:05 p.m. and lasted 10 minutes. Police officers found Campos when they arrived on the floor.

And since it is not Campos who summoned the police, it is once again unclear what event catalyze the end of the mass shooting.

Lombardo also disclosed that Paddock was seen on numerous occasions in Las Vegas without any person accompanying him and he gambled the night before the shooting. “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.

“In coordination with the FBI’s behavioral 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 key on,” Lombardo said.

Meanwhile, Sheriff Lombardo refuted something he himself insinuated last week, when he said that there is no indication anyone other than Paddock fired on the crowd: "We have uncovered no evidence to show there was a second shooter."

"We have uncovered no evidence to show there was a second shooter," Sheriff Joe Lombardo says of Las Vegas massacre https://t.co/Okz2bwUl4f pic.twitter.com/bNLOdsgyn3 — CBS News (@CBSNews) October 9, 2017

Now, as part of the new narrative, Lombardo said it was unclear why Paddock stopped firing at the crowd, suggesting he may have initially planned to escape. As we reported last week, Paddock also shot at jet fuel tanks at McCarran International Airport and had protective gear in the hotel suite and explosives in his parked car.