At Mandalay Bay, precious minutes passed before 1st call to police in Vegas shooting

— -- The first reports from hotel employees that there was a shooter in the Mandalay Bay hotel were not relayed to Las Vegas police until after the gunman had already begun the deadly rampage that killed 58 people across the street, according to a person who has reviewed the records and spoke to ABC News on the condition of confidentiality.

Stephen Paddock opened fire on a security guard, Jesus Campos, and a maintenance man, Stephen Schuck, down the hallway of the 32nd floor before he turned his attention to the concertgoers below. Both men called their supervisors, but neither the police account of the ensuing moments nor publicly transmitted police radio traffic indicate when the hotel security office dialed 911.

According to the latest police timeline, Campos was shot about six minutes before the rampage began. Hotel officials released a statement saying that timeline “may not be accurate.” Police say the current timeline will be revised again by Friday.

The new details of the moments before the deadliest mass shooting in modern American history came as the lawyer for one victim began asking the first uneasy questions as part of what is expected to be a rash of victims’ lawsuits focused on the initial response by the hotel.

“Was 911 called? The whole chain of command seemed to be broken down here,” said Mohammed “Mo” Aziz, a lawyer hired by shooting victim Paige Gasper. “For six minutes nothing happened, and then this criminal started shooting at innocent people.”

Hotel officials, however, believe the response by casino staff was swift and saved lives.

The lawyer’s questions Tuesday have put a new focus on the still-murky timeline for the moments leading up to the shooting. The shifting accounts from authorities first indicated a casino security guard was the last person to be shot before the shooter took his own life. Then they said he was the first to be injured.

New audio recordings made public by the hotel’s corporate owner, MGM Resorts, capture the chaotic moments when Schuck called dispatchers to report trouble.

“Call the police,” Schuck tells hotel security. “Someone’s fired a gun up here. Someone’s fired a rifle on the 32nd floor down the hallway.”

Officers did not reach the 32nd floor until at least 18 minutes after Campos was shot in the thigh, and they appeared to have no idea he had been wounded at all before finding him.

“They weren't aware of him being shot until they met him in the hallway after exiting the elevator,” said Clark County Sheriff Joseph Lombardo.

"We have a security officer also shot in the leg on the 32nd floor. He's standing right by the elevator," a Las Vegas Metro policeman radioed, in a recorded transmission 20 minutes after Campos was hit by Paddock's gunfire.

Assistant Sheriff Tom Roberts told reporters Monday that police are still studying the timeline, but he does not think the lag was long under the circumstances.

“I don’t think the delay, or the time lapse is that long -- in my opinion,” Roberts said. “I think the security guard saved a lot of lives -- he interrupted this guy and sped up his plan, in my opinion.”

In part, the response time may have been slowed by a decision to shut down the elevators, a move by hotel management described by Schuck in an NBC News interview. Some police had to climb an unknown number of flights of stairs carrying weapons and body armor.

At 10:16 p.m., an officer radioed his dispatch to "contact Mandalay Bay and have 'em shut down their elevators so he [the gunman] can't get mobile and we can take the stairs and block all the stair exits."

One officer was later heard on police radio traffic breathing heavily and announcing he'd made it up to the same level the gunfire was erupting from. “I'm in a stairwell on the 32nd floor,” he says in a hushed voice.

Sgt. Mike Quick, a retired Las Vegas SWAT team veteran, said the Mandalay Bay is a sprawling property, with a number of impediments.

“That's a 3,000-plus room casino hotel, I mean that's a major resort eating up acres and acres of property,’he said. “So just parking and getting through the front doors is going to be an exercise in time.”

Marshaling an elevator could have taken time, he said. But climbing the stairs was an “extreme challenge.”

MGM Resorts spokesperson Debra DeShong issued a statement Tuesday in response to the lawsuit filed on behalf of Paige Gasper.

This report has been updated to clarify that sources close to the Mandalay Bay hotel dispute the current official timeline and believe it will be revised.