Here's The New Moment-By-Moment Breakdown Of How The Las Vegas Shooting Unfolded

Law enforcement officials have changed a critical piece of the timeline in the Las Vegas mass shooting, saying that the gunman, 64-year-old Stephen Paddock, shot a hotel security guard before opening fire on a country music festival, rather than after the massacre as police initially claimed.

At a briefing on Oct. 13, Las Vegas Sheriff Joseph Lombardo said the timeline of when the guard at Mandalay Bay hotel was shot near Paddock's hotel room, when the hotel security team was notified, and when the mass shooting started, had not changed significantly.

He agreed with hotel owner MGM that the guard notified security staff seconds after being shot while attempting to breach a barricaded door to the 32nd floor near Paddock's hotel room.

Paddock fired 200 rounds at the guard, Jesus Campos, who survived his injuries, at 9:59 p.m., Lombardo said. Six minutes later at 10:05 p.m., Paddock opened fire, killing 58 below. By 10:17 p.m., 12 minutes later, officers had also arrived at the 32nd floor, by which time, the shooting had already stopped, Lombardo said.

Below is the moment-by-moment breakdown, according to officials.

9:59 p.m.: Hotel security is shot by Paddock outside his hotel room in the Mandalay Bay Resort and Casino

According to the latest official account of the shooting, Campos had been on the 32nd floor of the hotel Sunday night to investigate a door alarm, but turned toward Paddock's room when he heard what sounded like drilling.

Paddock — who had installed cameras to survey the hallway, and was believed to be drilling a hole to install another camera or rifle — shot Campos as he tried to breach a barricaded door on the floor, firing more than 200 rounds into the hotel hallway. He struck the security guard once, in the thigh.

According to Lombardo, Campos informed hotel security that he had been shot via radio about 40 seconds later.

Closed-circuit TV footage from the Route 91 Harvest music festival confirmed that the gunfire first erupted at 10:05 p.m. Sunday, as Paddock used modified rifles to spray automatic fire on the crowd below his hotel room.

Chilling footage from the scene shows country music star Jason Aldean, who had gone onstage 30 minutes before the shots began, continuing to play as the gunfire begins. People initially appeared confused about what they were hearing, before terror set in. The shooting continued for about 10 minutes.

The first fire truck arrived at the scene even before the first 911 calls.

"Our response time to that incident, I can honestly say, for our first arriving unit was less than five seconds," Clark County Fire Department Chief Greg Cossell said in a press conference Thursday.

Fire Engine 11, stationed about a mile from where the Harvest 91 country music festival took place, was driving back from a traffic accident when the firefighters heard gunfire. The engine captain, Ken O’Shaughnessy, immediately called dispatch, and asked if there were reports of gunfire because he could hear a lot.

"The captain was like ‘that’s gunfire,'" and quickly called dispatch to ask if there had been reports of a shooting, Cassell said.

Within moments, the gates of the festival opened "and out poured dozens and dozens of patients," the fire chief said. "Critically and some mortally wounded, and swamped that engine company sitting in the middle of the street."

O’Shaughnessy immediately called for a first alarm medical assignment, which brought in a brigade of EMS responders and ambulances, as well as a mass casualty unit.

As Paddock continued shoot into the crowd, police frantically worked to locate the source of the gunfire, even as they came under heavy fire themselves in the early minutes of the attack, according to radio dispatches and body cam footage from the scene.

"We're pinned down on the east side of Las Vegas Boulevard," one officer said over the radio. "We're taking gunfire. It's going right over our heads."

At 10:08 p.m., as initial reports of the shooting started to come in, officers were narrowing in on the Mandalay Bay, and by 10:12 p.m., the officers had closed in, arriving on the upper floors of the hotel, where they reported that the shots were coming from above.

"I'm inside the Mandalay Bay on the 31st floor," an officer said quietly on the radio. "I can hear the automatic fire coming from one floor ahead, one floor above us."

10:15 p.m.: Final shots fired

Police body camera footage pinpoints the last audible shot from the gunman at 10:15 p.m., a full 10 minutes after the shooting began.

It is not clear what prompted Paddock to stop the attack, which was over by the time officers arrived on this floor.

When police searched his room following the shooting, they found that he still had a thousand rounds of ammunition, and though some of the 23 guns he had with him had jammed, the 64-year-old still had plenty of firepower to keep shooting.

Authorities have said that they believe Paddock had planned to survive the shooting via some kind of escape, perhaps by exploding his car outside or fuel tanks at the airport, which sustained gunfire.

After police pinpointed the gunman's location on the 32nd floor of the hotel, the first two officers arrived on the scene.

"The officers in the first strike team reached the 32nd floor within 12 minutes, which is phenomenal, of the first shot being fired," Lombardo said.

Ten minutes after the last gunshot sounded, eight more officers arrived on the 32nd floor and began evacuating the other hotel rooms, and checking for anyone who may have sustained injuries.

"They could not hear additional firing," Lombardo said, but "they believed it was important to evacuate in case the suspect was barricaded."

10:55 p.m.: Tactical officers arrive in a stairwell near the gunman's room

A team of eight, including two K9 personnel, a SWAT officer, and patrol officers, all carrying tactical gear and rifles, approached Paddock's room, spotting the cameras the shooter had placed outside the suite.

Discharged rounds littered the hotel hallway, and through the holes in the hotel room door, officers could see a gun, Lombardo said. At that point, they were told to wait for backup.

"They pulled back and waited for the approach of a full SWAT team," Lombardo told reporters Wednesday, defending the decision to wait before entering the room. "Keep in mind the delay was not undue. It was purposeful, and no shots were being heard by the suspect at this point."

11:20 p.m.–11:27 p.m.: A SWAT team finally breaks into the shooter's room

More than an hour after the shooting began, police finally entered Paddock's hotel suite, after a SWAT unit set off an explosive device that allowed officers to breach the door.

They found Paddock on the floor, dead of a self-inflicted gunshot wound. It remains unclear when Paddock killed himself.

Inside the suite, officers were able to clear the first room, but found that the bedroom door was locked. Seven minutes later, they breached that door as well, confirming that the dead shooter was the only attacker.

Police later found 23 weapons inside the hotel room, including several assault rifles modified to shoot like automatic weapons. Paddock, who had checked into the hotel three days earlier, on Sept. 28, had brought the weapons to the room using "in excess of 10 suitcases," according to police.

About 20 minutes after clearing the second room of the suite, the Las Vegas Metropolitan Police Department informed the panicked public that the gunman was down.

A little over a half-hour later, the department sent out a second tweet, declaring that the incident was over.