Las Vegas police were in the Mandalay Bay Resort & Casino within minutes on Sunday evening as gunfire rang out from a room on the 32nd floor — but they didn’t enter the room of shooter Stephen Paddock for more than an hour. 

The heavily armed Paddock started his rampage at about 10:08 p.m., spewing fusillade after fusillade — enough rounds to kill 59 and injure more than 500 attending the Route 91 Harvest country music festival.

According to police radio transmissions, a group of officers was at the gunman’s door, and had locked down the 32nd floor, by about 10:25 p.m. but waited until about 11:21 p.m. — more than an hour after the attack began— before they blew open the door to enter, the recording shows.

“We need to pop this and see if we can incite a response from this guy to see if here’s in here or if he’s actually moved out somewhere else,” an officer says over radio dispatch as he readies an explosive on the door.

Several seconds later the officer warns others of the blast: “Breach, breach, breach.”

A loud explosion is heard over the radio.

It’s unclear why officers waited more than an hour to enter the gunman’s room. The delay has sparked questions about police response and whether officers should have breached the gunman’s room sooner. It’s also not clear when Paddock stopped shooting and whether officers were outside his room as the rampage continued. 

"I’m not sure why it took so long," said an expert on police tactics who was not authorized to speak with the media. "Your first priority is stopping the shooting and getting to the suspect."

Few details are available about the department's police tactics, but Clark County Sheriff Joseph Lombardo did say that when officers made it to the 32nd floor, they “received gunfire and they backed off and SWAT responded.” 

He said his officers are trained to deal with active shooters, but the Paddock case was “different ... because the active shooter (was) unreachable.”

“I’m very proud of what our officers did,” Lombardo said. 

The first officers to reach the 32nd floor found a security guard injured in the leg from one of Paddock’s rounds, fired through his hotel door. 

Experts say every second counts during an attack. The majority of active shooters finish their attack within five minutes or less, according to a study done by the FBI. 

The same study, which examined attacks from 2000 to 2013, found there had been 160 active shooter incidents within that time period. 

“You have to remember that this suspect knew what he was doing. He knew he could mask his fire and position with being at an elevated position,” said the expert. “It was a very calculated attack.”

The source said it’s possible the officers didn’t feel capable to stop the attack because of the Paddock’s high-powered weapons. 

A spokeswoman for the Las Vegas police said all officers are outfitted with bulletproof vests but the vests can’t withstand the highest-power weaponry. 

After the massacre at Columbine High School in 1999, law enforcement protocols were changed. During that attack, police waited for SWAT officers to respond, allowing the two suspects to continue their killing spree. 

The attack exposed flaws in standard police procedure, so protocols were altered to have first responding attempt to stop an active gunman. 

Police response is always critiqued after a high-profile attack. Orlando officers faced backlash after waiting about three hours to breach the Pulse nightclub last year after a gunman killed 49 innocents and injured at least 68 others. 

Police said they did not end the attack sooner because the gunman was holding victims, some of whom were critically injured, in a bathroom inside the club and did not want to cause more deaths.

That was not the case in Las Vegas.