A revised chronology given by investigators for the Las Vegas massacre is intensifying pressure for police to explain how quickly they responded to what would become the deadliest mass shooting in modern U.S. history.
Two hotel employees had called for help and reported that gunman Stephen Paddock sprayed a hallway with bullets, striking an unarmed security guard in the leg, several minutes before Paddock opened fire on a crowd at a musical performance, killing 58 people and injuring nearly 500 others.
At 10:05 p.m. Paddock began his 10-minute deadly barrage into the crowd, firing off more than 1,000 rounds, police said. Police didn’t arrive on the 32nd floor until 10:17 p.m., which is two minutes after he had stopped firing.
Questions remain about what happened in the six minutes between the time police say Paddock fired off 200 rounds through the door of his 32nd-floor suite into the hallway of the Mandalay Bay hotel and casino and when he unleashed a deadly hail of gunfire into the crowd at the Route 91 Harvest festival.
WATCH: Las Vegas police update timeline in mass shooting
Chief among them: Were police notified immediately about the hallway shooting and did officers respond quickly enough to have a chance to take out the gunman before could carry out the bloodshed?
How crucial were the minutes that elapsed before the massacre began? Here’s a look at what we know — and still don’t know — about the six minutes in question:
The chronology of the shooting has changed
On Monday, Clark County Sheriff Joe Lombardo said Paddock shot and wounded the security guard outside his door and opened fire through his door around 9:59 p.m. — six minutes before shooting into the crowd.
That was a different account from the one police gave last week: that Paddock shot the guard, Jesus Campos, after unleashing his barrage of fire on the crowd.
The sheriff had previously hailed Campos as a “hero” whose arrival in the hallway may have led Paddock to stop firing. On Monday, Lombardo said he didn’t know what prompted Paddock to end the gunfire and take his own life.
WATCH: Las Vegas Sheriff praises hotel security, police for stopping shooter
Bullets whizzing down the hallway
A hotel maintenance worker, Stephen Schuck, told NBC News on Wednesday that he told hotel dispatchers to call the police and report that a gunman had opened fire in the hallway on the 32nd floor.
He had been called there to check out a report of a jammed fire door and made it about a third of the way down the hall when he heard gunshots. Schuck saw Campos, the security guard, peek out from an alcove and was told to take cover.
He described bullets whizzing past his head as he tried to flee the shooting.
“It was kind of relentless so I called over the radio what was going on,” he said. “As soon as the shooting stopped we made our way down the hallway and took cover again and then the shooting started again.”
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Gunshots can be heard in the background as Schuck reported the shooting on his radio, telling a dispatcher: “Call the police, someone’s firing a gun up here. Someone’s firing a rifle on the 32nd floor down the hallway.”
Security guard is shot
Campos had been dispatched to the 32nd floor before Schuck to respond to an alarm that signalled a door was open and heard an odd drilling sound, police have said. As he approached there was a series of single gunshots through the door, one of which hit him in the leg.
At about the same time the maintenance worker arrived and Paddock fired more than 200 rounds through the door at Campos and Schuck.
As he was running away, Campos used his radio and possibly a hallway phone to call for help, Assistant Sheriff Tom Roberts confirmed to The Associated Press.
Hotel questions police timeline
Late Tuesday, a spokeswoman for Mandalay Bay questioned the latest timeline of events provided by police.
READ MORE: Stephen Paddock’s hotel neighbour details confusion, gunfire
“We cannot be certain about the most recent timeline that has been communicated publically (sic), and we believe what is currently being expressed may not be accurate,” said Debra DeShong, a spokeswoman for MGM Resorts International, which owns the Mandalay Bay hotel-casino.
The company’s statement did not offer what it thinks was the correct timeline.
WATCH: Las Vegas PD provide timeline on Mandalay Bay shooting
What typically happens when there’s a shooting at a casino?
A security officer in a casino-hotel the size of Mandalay Bay, with about 3,200 rooms, would typically report the shooting to an in-house dispatcher who would then call Las Vegas police, said Jim Tatonetti, an executive with Griffin Investigations, a Las Vegas company that provides security and surveillance information to casinos.
Tatonetti said they should have gotten word quickly about the shooting from the lead hotel security supervisor or they would hear the call from police dispatch.
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“When you have law enforcement on property you defer to them,” Tatonetti said, adding that hotel security officers would turn to their primary duty: guest safety. Officers would focus on evacuating and keeping guests away from dangerous areas.
A large casino in Las Vegas might have 50 or more security officers on a shift, Tatonetti said. Supervisors might be armed. Few on regular patrol have guns. Some might have emergency medical training.
What we still don’t know
It was unclear if the hotel relayed the reports of the hallway shooting or the gunman’s location to the police.
The Las Vegas Metropolitan Police Department hasn’t responded to questions from The Associated Press about whether hotel security or anyone else in the hotel called 911 to report the gunfire. Police have not responded to questions about the hotel’s statement or whether investigators stand behind the revised timeline released earlier in the week.
A request for the 911 recordings was denied by police who said they were part of the ongoing investigation.
*Associated Press writer Ken Ritter in Las Vegas contributed to this report