It was a relatively quiet night near the Vegas strip on Sunday night when the first call came in about the mass shooting at the Route 91 Harvest Festival.

“We knew there had been a shooting, but we didn’t know that it was a mass casualty,” Dean, a 31-year-old paramedic, tells PEOPLE. “We headed over to help out.”

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When they arrived near the Mandalay Bay Casino, Dean and his partner saw dozens of ambulances waiting. “That’s when we knew it was really serious,” he said. “The cops were telling me that we couldn’t go to the area yet, because it wasn’t secure. They wanted to make sure that we weren’t going to be targets. So we had to wait for an area to be cleared before we could go help.”

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When paramedics and EMTs were finally able to get to an area where people lay injured, they were accompanied by police officers with their guns drawn. “There were cops all around the perimeter of the area to provide cover in case we needed it,” he says. “I had never been so scared in my life. I just kept thinking the shooting would start up again.”

The injured had been tagged with color-coded stickers on their bodies by a first responder team doing triage. Patients tagged in green had minor injuries. Those with yellow tags had non-life threatening injuries. A red tag meant that the patient had life-threatening injuries and needed to be transported immediately to a hospital. Those tagged in black were dying or expecting to die.

“We had to take the red-tagged patients first,” he says. “But it’s not always that easy. People were begging me to take them because they were in so much pain. One woman grabbed at my ankle and we locked eyes. All she could say was ‘please.’ She had tears all over her face. But she was tagged in yellow, and there were people in red. So I had to say, ‘I’m so sorry. Someone will be back for you soon.’

There was another man who was tagged green sitting next to a yellow,” he continues. “He said, ‘please help my girlfriend,’ but I couldn’t.”

The first patient they took was a woman with a gunshot wound to the chest. “She wasn’t able to breathe,” he says. “She was in really bad condition. We took her to the [ambulance] and to the hospital. Dispatch told us to go right back for more patients.”

He does not know if the woman survived or not.

58 people were killed in the attack, and another 527 were hospitalized, authorities have said.

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“After that point, dispatch was out of the picture,” he says. “There were officers on the scene who were directing what to do. It was pretty clear that we had to take injured people to the hospital, in order of the severity of their injuries. So that’s what we did.”

On their second pickup, patients were getting more desperate. “They’d been waiting for maybe 20-30 minutes at that point, and they’re hurt and they’re bleeding,” he says. “So as you walked past them, they’d be like, ‘Help me, please. Help me.’ There was a man tagged yellow who said, ‘I have a new baby. Please save me.’

“You have to understand that yellow tags can become red really fast,” he says. “They’re all losing blood. They’re in pain and going into shock. So it’s not like he was being dramatic. I’m sure he thought he was going to die. And maybe there was. We had to make quick decisions.”

“There were officers helping us triage, but there was still some discretion. Do I pick up this red tag or that red tag? Which patient do we take? What if we choose the wrong one? It can be agonizing.”

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As he took multiple trips, Weber says that there seemed to be an endless number of critical patients. “By now, some of the yellow tags were doing really bad. They had deteriorated. We were just trying to save as many lives as we could.”

“The night was endless,” he says. “This morning, we were still taking patients to hospitals, but they were mostly green — things like people who had been trampled and had broken arms or ribs. They had been waiting for hours, so they had all that time to sit on the ground, injured. The people they were with had been taken away, and they had no idea if their husbands or sisters were alive or dead. One woman just wailed the whole way to the hospital, not from pain, but from fear.”

Dean estimates that he took about 15 patients to the hospital from the scene. (PEOPLE spoke with two employees at the Southern Nevada Health District who could not verify Dean or this particular account, but said it seems consistent with the events of the evening.)

“When it was over, I just hugged my partner and cried,” he says. “It was overwhelming.”

“It was like a war zone,” he says, his voice starting to crack. “It’s the worst thing I’ve ever seen in my entire life, and I hope that no one ever has to go through it again. It was pure hell.”

How to Help and Learn About Loved Ones

Friends and family are asked to report missing people believed to be connected to the shooting using the hotline 1-800-536-9488.

Anyone with photo or video evidence of the shooting is asked to call 1-800-CALL-FBI.

The city of Las Vegas has established a Family Reunification Center to help connect relatives with the more than 500 people who were injured.