A veteran police officer’s self-described freeze in a Las Vegas hotel hallway while a gunman fired on an outdoor concert crowd is prompting a review of whether lives could have been saved if officers had acted faster to stop the deadliest mass shooting in the nation’s modern history.

Three police tactics experts said they understood Officer Cordell Hendrex hesitating as he led a trainee and three Mandalay Bay hotel security guards toward the sound of rapid gunfire Oct. 1.

“We teach officers to respond directly to the active killing. Every second that it continues to go on, more lives are at risk,” said J. Pete Blair, a criminal justice professor and director of the Advanced Law Enforcement Rapid Response Training center at Texas State University. “But we don’t expect them to take unnecessary risks.”

Carla Alston, spokeswoman for Clark County Sheriff Joe Lombardo, issued a statement last week saying that every officer’s actions during the massacre was being evaluated by the department.

Hendrex acknowledged being “terrified with fear” in a written police report submitted Oct. 7 and made public May 23 by the Las Vegas Metropolitan Police Department under court order.

“I froze right there in the middle of the hall for how long I can’t say,” he wrote.

The video and report represent separate parts of a massive puzzle being pieced together by authorities who say they’ve found no motive for the gunman’s rampage.

The footage was part of the eighth release by police of heartbreakingly graphic sights and sounds of the massacre and its aftermath. A ninth release is due Tuesday.

Hendrex, a nearly 10-year department veteran and field training officer, is first seen teaching rookie Officer Elif Varsin to write trespassing tickets for two women in a Mandalay Bay hotel security office.

Amid radio reports of ongoing shooting and “multiple casualties,” Hendrex, Varsin and three Mandalay Bay security officers run to an elevator talking about a shooter on the 32nd floor. They get off on the 31st floor. The reason has not been explained.

In the footage, Hendrex leads Varsin and the security guards, each with handguns drawn, out of the elevator and down a 31st floor hallway. They hear the first of at least five separate volleys of rapid gunfire during a three-minute span.

“Holy s—. That’s rapid fire,” Hendrex says. The group stops.

“I’m inside the Mandalay Bay on the 31st floor, we can hear it above us,” Hendrex says over his police radio.

“Just be advised it is automatic fire, fully automatic fire from an elevated position,” a radio voice says. “Take cover.”

Varsin’s video shows the group in the 31st floor hallway for about five minutes before Hendrex leads them halfway up a stairwell to the 32nd floor. They remain there for at least 15 minutes, when the video clip ends.

Authorities have said the gunman, Stephen Paddock, fired barrages for about 10 minutes from 32nd floor windows into the open-air Route 91 Harvest Festival concert across Las Vegas Boulevard before killing himself. More than 400 people were wounded and hundreds more were injured as they fled, officials said. Fifty-eight people were killed.

“I remember thinking that I had myself, my day 2 trainee and three security managers,” Hendrex later wrote. “Between the 5 of us only I and Officer Varsin were wearing body armor and all of us were armed with a handgun each.”

“The shooting stopped and all I could think was to stop the shooter or shooters from … escaping,” he said.

It is not clear if Hendrex reached the 32nd floor stairwell door near the shooter’s room that had been sealed shut. On the 32nd floor, a hotel security guard had been wounded in the leg by gunshots fired through the door into the hallway where he had discovered the obstruction.

Body-camera video released May 2 shows teams of officers sometime later moving carefully from different locations, checking rooms on floors 29, 30 and 31 before blasting through the door to Paddock’s suite. That was about 80 minutes after Paddock started shooting, and more than an hour after gunfire ended.

Inside, police found Paddock dead, windows broken and 23 rifles strewn about. Fourteen of the rifles were fitted with “bump stock” devices to allow rapid-fire shooting similar to that of automatic weapons.

Questions were raised amid changing timelines from Las Vegas police and the FBI in the days after the shooting about why police didn’t get to Paddock sooner.

Lombardo said at that time he was “absolutely offended” by suggestions that police bungled the response.

Lombardo, who has since been re-elected head of the police department, ordered officers and employees not to comment about what he calls an ongoing investigation. The FBI in Las Vegas has repeatedly declined to comment.

The sheriff has said he expects a final report to be issued by August.

Hendrex and Varsin did not respond to email messages from The Associated Press, and Steve Grammas, head of the police union, declined to comment.

Eugene O’Donnell, a former New York police officer who teaches at John Jay College of Criminal Justice in New York, called for “an honest conversation about the need for police to transform on a dime from peacekeepers to military commandos.”

“We have to be realistic,” O’Donnell said. “Police officers are civilians with guns. The notion that they can spring into action and take on a mass murderer who is running up the body count is probably something you can’t ask.”

Thor Eells, executive director of the National Tactical Officers Association, viewed the body-camera video at the request of AP.

He said no amount of tactical training and crisis conditioning, short of actual combat experience, can overcome a natural reaction to pause in the face of danger.

“This is not a training issue,” Eells said. “You can simulate an active shooter scenario, but it’s not the same as when real bullets are flying.”

(AP)