When Orlando police officers and other law enforcement officials flooded Pulse nightclub last summer after a shooting rampage, they encountered a horrifying scene reminiscent of a war zone.

Nearly half of the 49 people who would die during the massacre and hours-long standoff that followed were on the dance floor and a nearby stage. There were so many bodies massed on the floor that after police went inside, an officer had to announce: “If you’re alive, raise your hand.”

That account comes from a presentation Orlando Police Chief John Mina has given about the shooting on 10 occasions, including to law enforcement leaders in California last year.

This presentation, first reported by the Orlando Sentinel and obtained by The Washington Post, provides a grim timeline of the deadliest mass shooting in modern American history and how law enforcement officers responded.

Many details in the 78-page presentation were reported by The Post last summer, in a story that detailed both the law enforcement response and the movements of Omar Mateen, the gunman who opened fire inside Pulse on June 12. Other information was included in 911 dispatch logs released by police or other news stories that followed the shooting.

The presentation provides what the Orlando police view as the key moments in the attack and their response as well as what appears to be new information. Mina’s presentation states that by 2:35 a.m. — the same time the FBI said Mateen made contact with 911 and pledged allegiance to the Islamic State — police said they had taken nearly all of the critically injured victims from the club. The only exceptions were the people being held hostage by Mateen inside the bathrooms, where he remained holed up for hours, as well as a dozen people hiding in dressing rooms.

Orlando Police Chief John Mina discusses the shooting last summer. (Chris O’Meara/AP)

After Mateen retreated into a bathroom, police did not pursue him, which gave way to the standoff that lasted until a SWAT team began breaching the club walls after 5 a.m.

This meant that injured victims remained trapped inside the bathrooms for hours with Mateen, who police say began firing shots inside one bathroom after police first made a failed attempt to breach the club wall with an explosion. Witnesses have told The Post that Mateen appeared to shoot people inside the bathroom before police successfully breached the club with an armored vehicle.

Witnesses and relatives have identified at least five people who were alive in the bathrooms when the standoff began but died at the club. Three of them had sent text messages from inside the bathrooms.

One victim — 18-year-old Akyra Murray — called 911 from the bathroom, telling a dispatcher at 2:36 a.m. that she was losing feeling in her body. According to Mina’s presentation, another person called 911 after 4 a.m. to say that Mateen appeared to have a bomb strapped to him. Not long after, a victim inside the bathroom sent a text message to her brother saying that Mateen “was going to strap four bomb vests to hostages in 15 minutes,” Mina’s presentation notes.

Mina’s presentation states that among the 49 people killed, 13 were found inside the bathrooms where hostages were held. Another 20 were on the dance floor and stage area, and three others were on the stage. Others were found in the lobby area, the patio or died once they were taken from the club.

This presentation does not say whether any of the victims were killed by police gunfire. A police spokesman declined to answer that question Friday, citing the ongoing investigation into the incident. Mina has previously said he did not know whether law enforcement officers inadvertently killed any of the victims.

According to Mina’s presentation, police rescued “approximately” 18 victims from both bathrooms after breaching the club walls. Mina had told The Post last year that 15 hostages were freed from one restroom and three to five escaped from another.

“I have no regrets in the decisions that my officers and commanders on the ground made, and I have no regret with the decision I made, either,” Mina said in an interview last summer.

Mina said in the interview that police did not pursue Mateen into the bathroom because he had stopped shooting, shifting him “from an active shooter to a barricaded gunman.”

Mina’s presentation states that after SWAT teams breach the northern bathroom wall and deployed two flash-bangs, Mateen was drawn out to the hallway and fired multiple times at officers.

The SWAT team returned fire, with one of them killing Mateen. One round hit the helmet of a SWAT member. A photo of that helmet has been widely circulated. Mina’s presentation includes what appears to be a still from a body-worn police camera showing that officer being treated for a large, bloody injury on his forehead.

The law enforcement response to the shooting will be studied by other police departments as they try to train their officers about how to react to the next possible mass shooting. The Justice Department is reviewing the Orlando response at the request of the local police force.

Such reviews have followed other attacks, including the shooting rampages at the Virginia Tech campus, the Washington Navy Yard and a movie theater in Aurora, Colo., and in each case, officials found ways to improve their responses.

In Mina’s presentation, he notes that within minutes of the attack, “the triage area is becoming chaotic with victims and witnesses.”

The presentation also hints at the breadth of the FBI investigation into the shooting, with Mina saying that more than 300 subpoenas had been issued, about 500 interviews completed and nearly 1,000 pieces of evidence collected.

Nearly a year after the shooting, the probe has resulted in one arrest. The FBI arrested Noor Salman, Mateen’s wife, in January and charged her with aiding and abetting terrorism.

Last month, survivors of the Pulse attack filed a federal lawsuit against Salman and Mateen’s former employer, arguing that the massacre could have been prevented had they responded to his behavior.

Further reading:

‘He said he cannot get out’: 911 calls during Pulse shooting show terror, frustration

Orlando hospitals say they won’t bill Pulse shooting survivors

‘How did I walk away alive?’ The Orlando shooting through a survivor’s eyes.