Curtains blow out of broken windows at the Mandalay Bay Resort and Casino, facing the scene of the mass shooting at the Route 91 Harvest festival. (Paul Buck/European PressPhoto Agency-EFE/REX/Shutterstock)

Lying on the floor of his hotel room and wincing at the sound of gunfire, Ben Sweeney pecked out a text message to his wife but did not hit send.

Babe I think someone is shooting here I’m really scared it’s loud 

(Ben Sweeney)

The gunfire sounded like it was coming from the room next door, Sweeney told The Washington Post. His mind raced to the worst possible scenario: an active shooter, kicking in doors, killing random hotel guests.

But the Mandalay Bay Resort and Casino is huge, and so is Las Vegas, and Sweeney didn’t want to scare his wife — asleep back home in Pennsylvania — until he knew what was going on.

They had just said their good-nights. Sweeney was attending an IT conference that started the next day. He’d checked into the hotel around 6 p.m., walked around a bit and listened to the country music concert going on 30 floors below.

His wife is a country music fan. He is not. So before turning in, he held the phone up in the air to let her hear the music and crawled into bed.

Then he heard booms.

He assumed it was fireworks connected to the concert, he told The Post, and figured he might as well catch a glimpse before turning in.

He opened the curtains, but instead of lights in the sky, he heard more booms, closer together, from the hotel.

“That’s a machine gun,” he thought, dropping to the floor. “An automatic rifle.”

The booms were tightly grouped. Seven at a time. Five at a time.

“It seemed like I was so close,” he told The Post. “I thought it was coming from the room next to me. I could hear the shots go off inside the hotel first, then echo outside.”

He made sure his door was locked, turned off the TV and crawled into the bathroom. There, inside whatever safety the tub provided, he looked at his phone and hit “send.”

Now, both Sweeneys were worried, but neither knew what was going on — or what to do.

Sweeney sent his wife a picture of the ground below the hotel, but it was too far away to show any detail. Then he sent her an audio file, but she couldn’t really hear it.

His realization came a few moments later:

(Ben Sweeney)

Ya hun It’s an active shooter I swear it’s right in the room next to me. 

It’s so loud and it echoes It’s a machine gun

Sweeney and his now-fully-awake wife cobbled together what was going on from Twitter and Facebook and news reports.

A man opened fire from the 32nd floor of the hotel — two floors up and one room over from where Sweeney huddled in the bathtub.

The shooter had almost the same view that Sweeney had, and he was firing indiscriminately into the crowd.

At least 58 people were killed by gunfire, and more than 500 were wounded. The victims were attending the Route 91 Harvest festival.

But Sweeney was safe.

He texted his parents, figuring they’d wake up, hear the news and worry. And he whispered to his wife on the phone.

Occasionally, he crept over to the bed. Afraid that the TV would attract a shooter, he checked social media on his laptop for information.

At one point, “all of a sudden I hear this loud explosion,” he told The Post. It was also from inside the hotel.

Police in Las Vegas said their SWAT team used explosives to get into the room where the shooter, Stephen Paddock, had fired from.

Paddock was an accountant with real estate investments around Orlando and “plenty of money to play with,” a family member said. He killed himself as SWAT officers closed in. The investigation into what has been called the worst mass shooting in the modern era is ongoing. On Monday, police were working to identify the dead.

Around 4:30 a.m., Sweeney was awakened by officers at the front door who said they wanted to do a welfare check. He assented and they burst in, checking the closets and the bathroom with guns pointed, clearing the room. When they left, he heard similar shouts and commands as the officers moved on.

Ben and Allison Sweeney (Courtesy of Ben Sweeney)

By the time the sun came up, he said, the IT conference was an afterthought. He just wanted to be out of Las Vegas.

He booked a flight to Newark. His wife was going to drive 90 miles to pick him up.

Before he left the hotel, less than a day after checking in, he glanced outside the window. In the daylight, he could make out the police activity 30 floors below.

And he could see white tarps. There were dozens of them. Under each, he assumed, was a body.

“If I look out my window right now, I see the tarps out there. The aftermath. You see the tarps, and you know someone went out there to have a good time in Vegas and never went home.”

Read more: 

A fire alarm from gun smoke led police to the shooter’s room, retired officer says

Route 91 Harvest festival: The Las Vegas ‘sleepover’ that ended in a nightmare

How far-right trolls named the wrong man as the Las Vegas shooter

Gunman enjoyed gambling, country music, lived quiet life before massacre

How a Domino’s pizza crust led police to a suspect in mysterious D.C. slayings

After shootings, police fear being ‘a public target’ — even at lunch