LAS VEGAS >> Rob Ledbetter’s battlefield instincts kicked in quickly as bullets rained overhead.

The 42-year-old U.S. Army veteran who served as a sniper in Iraq immediately began tending to the wounded, one of several heroes to emerge from the deadliest mass shooting in modern U.S. history. Amid the massacre in Las Vegas, which left 59 people dead and more than 500 injured, there were acts of compassion and countless heroics that officials say saved scores of lives.

There was a man one survivor knows only as Zach who herded people to a safe place. There was a registered nurse from Tennessee who died shielding his wife.

Like many people in the crowd of some 22,000 country music fans Sunday night, Ledbetter heard the pop-pop-popping noise and figured it was fireworks. Then he saw people dropping to the ground. When more booms echoed in the night air, he recognized the sound of automatic weapons fire.

The gunman, identified as Stephen Craig Paddock, a 64-year-old retired accountant from Mesquite, Nevada, created his own sniper’s perch inside the 32nd-floor room at the Mandalay Bay casino hotel, across from the concert grounds. He appeared to fire unhindered for more than 10 minutes, according to radio traffic, and then killed himself before officers stormed in and found 23 firearms.

“The echo, it sounded like it was coming from everywhere and you didn’t know which way to run,” said Ledbetter, who was at the concert with seven people including his brother, who was shot and injured, and his wife. They found cover in a VIP area of the concert. Once out of harm’s way, he turned to injured strangers.

Thanks to a man who took the flannel shirt off his back, Ledbetter says he put a makeshift tourniquet on a wounded teenage girl, whose face was covered with blood.

“Some random guy, I said, ‘I need your shirt,’ “said Ledbetter, who is now a mortgage broker and a resident of Las Vegas. “He just gave me the flannel off his back.”

Ledbetter said he compressed someone else’s shoulder wound, and he fashioned a bandage for a man whose leg was shot through by a bullet.

“There was a guy that looked like he had a through and through on his leg, that we just put a T-shirt around and just did a bandanna tie,” said Ledbetter, who was outside University Medical Center on Monday, where his brother was being treated for a gunshot that went through his arm and into his chest. He is expected to survive.

Ledbetter and others grabbed the injured man, carried him out to Las Vegas Boulevard, put him in the back of a utility truck with five to 10 other people that was headed to the hospital.

Ledbetter said he would have helped more people but couldn’t clear the barrage of gunfire.

“I’m saving people, or trying to do my best. But it got to the point, I saw people all over, laying where we used to be standing … just laying there and nobody getting to them and I couldn’t get out there. The shots just kept coming in and bouncing. I would have been in harm’s way,” he said.

He worries that those unfamiliar with battlefields will suffer what they have survived.

“Everybody there is going to have emotional problems. I know that. There was blood everywhere I went: Excalibur, Luxor, on the Strip, on the street,” Ledbetter said. “All these people are going to have PTSD. I feel bad for all of them.”

Another concertgoer, Anna Kupchyan, credits a man she knows only as Zach for saving her life and about nine others when he herded them into an outdoor trailer serving as a restroom.

Kupchyan, a 27-year-old law student from Los Angeles, said bullets were raining down on the crowd as she and a horde of others began running in search of a way out of the outdoor venue.

The man, Zach, opened a door and ordered people inside and then joined them and shut the door, Kupchyan said.

They stayed inside as the shooting continued, everyone paralyzed in fear, she said.

“Then security came and they shouted for us to get out, to run,” she recalled. Outside the trailer, dead bodies were sprawled on the ground, including a man who had been shot in the head, she said.

She and her best friend Leslie Aguilar, a 26-year-old therapist, eventually jumped in a cab that was driving by and befriended two other women survivors who let them stay in their hotel room until the danger subsided.

Not all of Sunday night’s heroes survived.

Sonny Melton, a registered nurse, died in the shooting, according to The Henry County Medical Center in Paris, Tennessee, where he worked.

His wife, Dr. Heather Melton, an orthopedic surgeon who was with him when shots were fired, survived.

She told WZTV in Nashville, Tennessee, that her husband “saved my life and lost his.” She said her husband was the most kind-hearted, loving man she ever met.

Associated Press Writers Jocelyn Gecker in San Francisco and Anita Snow in Las Vegas contributed to this report.