Standing to the left of the stage where country singer Jason Aldean had just started performing, Debby Allen dialed her son’s number. They were supposed to go to the concert together Sunday, the last night of the Route 91 Harvest music festival, but Allen had overslept after a long day at the pool. When she woke up in their hotel room, she called her son, Christopher Roybal, who told her he was already at the concert.

“I’m here, where are you?” Allen said as she stood by a trailer. Roybal, who was on the other side of the stage, couldn’t hear her, so she decided to just find him after the concert.

They would never meet. That long day at the pool was the last time she spent with her son, whose coming birthday they were celebrating that weekend.

About 10 p.m., just a few songs into Aldean’s set, bullets began to rain down on the crowd of more than 22,000 people. Allen and her friends ran after a woman to her left was shot. The bullets kept coming, the gunfire seemed never-ending. She was still not sure what was going on, but she and her friends just kept running toward an exit.

As soon as they reached the street, Allen realized that her son was not with her.

“My son, my son is still there!” she screamed to a stranger wearing an American flag shirt.

“You cannot go back toward the gunfire,” she remembered the man telling her.

“I can’t leave here without my son,” she said, as she tried to force her way back in.

But the man stopped her. “You’re gonna get hit with gunfire and your son’s not gonna have you,” he told her, promising he’d go back and find her son for her.

Allen never saw that man again.

Authorities would later say that the deadliest mass shooting in modern U.S. history was carried out by a man who fired from the 32nd floor of the Mandalay Bay Resort and Casino. Stephen Paddock, who authorities say killed 58 people and injured hundreds of others, was later found dead in his hotel room.

Allen was screaming and crying as she and several others walked to the nearby Desert Rose Resort, where they stayed for several hours to escape the chaos outside. Allen had called her son over and over, but he never picked up. She knew then that he was hurt. Roybal would have answered her calls. He would have called her to make sure she was all right.

She and Roybal were not just mother and son. He was her firstborn, her “Munchkin”  who grew up to become her best friend. They watched and cried over chick-flick movies together. He loved to serenade friends with Spanish ballads. He went to a war zone to serve his country.

“I knew. I just knew,” she said. “I knew that I was never gonna see my son in my life. My heart told me.”

Later that night, one of Roybal’s friends, a firefighter named Mike, called to tell her that Roybal had been shot in the chest.

“I saw the life go out of him,” he told her, according to Allen.

Her knees weakened. Again, she was screaming. “My son! My baby boy!” Strangers held her tightly as they sat around her on the floor of the hotel lobby.

Allen’s cousin later picked her up and drove her to the nearby University Medical Center, but she said they were not allowed to get in. Then, they went to the Las Vegas Police Department headquarters. Allen wanted someone — anyone — to tell her that her son had been given first aid, that his name was on the list of victims being treated at the hospital, that his friend was wrong.

“I waited and waited and waited and waited, and the next day came by,” she said. “I begged the coroner. I said I need to know. I don’t want to know that he’s dead . . . but I just need to know.”

The coroner asked if her son has special markings that would help identify him. Roybal had plenty, Allen responded. Both of his arms were covered with tattoos. He had a military dog tattoo on his chest, the word “Mom” on his hand, the Lord’s prayer on his side.

Allen, again, waited some more, and later made her way to the Las Vegas Convention Center, which Clark County authorities had turned into a facility to help families identify their loved ones. There, she received an update from the coroner.

Authorities had matched Roybal’s fingerprints taken during his military service with one of the bodies they had recovered, the coroner told her. Again, Allen’s knees weakened, and again, she fell to the floor screaming for her son.

Roybal, a manager at a Crunch Fitness gym in Colorado, would’ve turned 29 Monday. He was a Navy veteran who served as a dog handler in Afghanistan. Last July, Roybal wrote on Facebook about his time there. He talked about the sensory overload, the adrenaline rush, the excitement, the anger brought by constantly being close to death.

“Unfortunately, as the fights continue and as they increase in numbers and violence, that excitement fades and the anger is all that’s left,” he wrote in the lengthy Facebook post that has been shared hundreds of times since his death.

“The anger stays, long after your friends have died, the lives you’ve taken are buried and your boots are placed neatly in a box in some storage unit. Still covered in the dirt you’ve refused to wash off for fear of forgetting the most raw emotions you has a human being will ever feel again.”

Roybal enlisted in 2007, according to the Pentagon. Allen tried to talk him out of it. They’re not a military family, she told him, and she didn’t want her son to be killed. But Roybal had insisted that it’s what he needed to do.

He left on a medical discharge in 2012, when he had become mostly deaf in his left ear because of all the explosions that happened near him, Allen said. Roybal took home a handful of medals and ribbons. But it seemed he also brought with him a lasting, emotional scar.

“What’s it like to be shot at?” he wrote on Facebook. “It’s a nightmare no amount of drugs, no amount of therapy, no amount of drunk talks with your war veteran buddies will ever be able to escape.”

But for Allen, Roybal was more than just a wounded veteran. He was a lovable son who loved chick flicks just as much as she does. He cried after watching “The Notebook.” She said it was one of his favorites. He also loved “The Story of Us.”

Before Roybal moved from California to Denver last spring, he and Allen went out to dinner and watched “Beauty and the Beast.” That made him cry, too.

He also loved karaoke and Spanish ballads. Luis Miguel and Christian Castro were his favorite singers. At age 2, he was singing Frank Sinatra.

“He’d sing these songs to his female friends, and they would just love it,” Allen said.

In fact, she said, Roybal never heard a song he didn’t like. But country music was his favorite.

Every morning on his way to work, Roybal would call his mother for no special reason other than to just talk.

“Mom, I love this song. Hang up the phone, go listen to it and call me back,” he would tell his mother during one of their conversations.

Allen, who’s divorced from Roybal’s father, has three other children, a 22-year-old daughter, and two sons, 19 and 6. Although her children’s ages are far apart, they were each other’s best friends. In fact, Roybal was a best friend to a lot of people. Allen said she’s heard from many of them, one of whom had started a GoFundMe page to help pay for funeral costs.

“They keep calling me and they cry . . . and they tell me how much he loves me. ‘He’s told us so much about you. He loves you so much,’” she said, remembering conversations with Roybal’s friends.

Allen is still in Las Vegas, waiting for authorities to release her son’s body before she could go home to California.

The last few nights were like a nightmare that she wants to wake up from.

“I only know that my heart’s in a billion pieces. He’s never gonna be home again,” Allen said, her voice breaking. “He’s never gonna be 29 years old.”

More than anything, she wants her son to call her, to tell her that he was okay, and that he was just on his way to work.