On a sweltering weekend evening, beneath a clear blue sky, Donald Trump supporters in red “Make America Great Again” hats packed the fairgrounds in Butler, Pennsylvania.

It was a friendly and festive venue for the once and maybe future president’s final rally before the Republican National Convention the following week. He won Butler County, just north of Pittsburgh in the crucial swing state, by roughly 2 to 1 in both 2016 and 2020.

“God Bless the U.S.A.” boomed over a speaker — “I’m proud to be an American, where at least I know I’m free” — as Trump arrived wearing his own red MAGA hat. He stood before a row of gold-trimmed American flags. He waved, clapped and pointed to his fans, their cell phones held aloft to record him. The peaks of white tents rose near the red, white and blue-striped grandstands. A green farm combine sat to one side of the rally.

To retired emergency room doctor James Sweetland, it felt like “an old-time rock concert.” As they awaited Trump’s appearance, Sweetland helped a fellow attendee who was suffering in the day’s heat, advising her to lie down and giving her water until emergency crews arrived. At the time, he said, it felt like the worst that could happen.

Joleen Monteleone, 57, of Butler, was in the bleachers behind Trump, wearing a “Trump 2024” denim vest that her husband made. Kristen Petrarca, 60, was there, too. “I’d never been to a rally,” she said, “and I really wanted to just experience it.”

The former president climbed three steps to the stage, basking in applause and chants of “USA!” before delivering a familiar litany of grievances against the news media, President Joe Biden and immigrants living in the country illegally. He reiterated his false claims that the 2020 election was rigged against him.

6:02 p.m. ET: Trump takes the stage in Butler, Pa.

He pointed to a large video screen depicting statistics on border crossings. Sweetland was sitting near the foot of the screen and felt like Trump was looking right at him.

In the seconds that followed came chaos.

Confusion, then panic

Less than 200 yards (meters) away, unknown to Sweetland or Trump, another scene was playing out.

Some rally-goers had noticed a man climbing to the roof of a nearby building. A local police officer climbed up after the man, but retreated back down the ladder when the man pointed his gun at the officer, two law enforcement officials told The Associated Press on the condition of anonymity so they could discuss an ongoing investigation.

Then: shots. Confusion. Disorder.

Around 6:10 p.m. ET: Shots fired at the rally

Trump grabbed his right ear. He ducked. A cluster of Secret Service agents in dark suits piled atop him, ready to take a bullet. More shots.

“Get down!” some rally-goers shouted as others ducked. Still others tried to keep their cell phone cameras pointed at the chaos onstage.

“Everybody was just like screaming and trying to hide in between the bleachers,” Petrarca recalled. “And I’m literally being pushed down, in between the bleachers, where your feet would be.”

Trump’s microphone picked up the urgent chatter of the Secret Service agents.

“I got you, sir! I got you!”

“Shooter’s down.”

“We’re clear, we’re clear.”

“Let’s move!”

The agents helped lift him to his feet, his hat knocked off and his hair mussed. They continued surrounding him. As they began to usher him off the stage, Trump paused. He wanted to get his shoes. Then he paused again.

“Wait!” he shouted. “Wait, wait, wait.”

With blood covering his ear and streaking across his face in two rivulets that converged on his tightly pressed lips, he looked out past the agents to the stunned but adoring crowd — and pumped his fist. Even in the middle of the shocking attempt on his life, the former reality TV star’s instincts for showmanship and symbolism did not fail him.

“Fight!” he mouthed. “Fight! Fight!”

The agents moved him into a black SUV. All around him, his supporters erupted in chants.

“USA! USA!”

Around 6:12 p.m. ET: Trump is moved to a vehicle

A jumbled aftermath

The Secret Service said its snipers had killed the gunman after the assassination attempt. But even now, two days later, the attacker’s motives and actions in the hours before the shooting are unclear.

His name was Thomas Matthew Crooks, 20, a nursing home employee from the suburbs south of Pittsburgh. He’d been armed with an AR-15 that his dad bought.

Crooks did not kill Donald Trump. But in those moments, another life was lost.

Corey Comperatore, a 50-year-old former fire chief who had served for decades with the Buffalo Township volunteer fire company, was in a section of bleachers just to Trump’s right. At the pops of gunshots, he dove to cover his wife and daughter. A bullet struck his head.

When Sweetland, the retired ER doctor, heard calls for help nearby, his muscle memory kicked in. He rushed to the grievously wounded Comperatore and performed CPR as blood seeped from a hole above the man’s right ear. Two minutes into his efforts, state troopers tapped him on the shoulder, took over, and then picked Comperatore up “like a rag doll” and carried him off on a stretcher.

“I looked up and I saw what I assumed would be his wife and a daughter that were there, and the look on their face was something I’ll never forget,” said Sweetland, who is from a town called DuBois about 90 minutes away. “The look on their faces, they were appalled, they were sad. And the look on everybody’s face in this situation is, ‘Is he gonna be alright?’

“And all I could blurt out was, ‘They’re taking him to where he can get help.’”

Rico Elmore, vice chairman of the Republican Party in neighboring Beaver County, also heard the cries for help. He removed his tie and rushed over a barricade toward the wounded man. He held the man’s head with a towel.

Later, in an interview with The Associated Press, Elmore pulled a red T-shirt over his white shirt, which was stained with the victim’s blood. “It was a horror,” Elmore said. “I pray to the family that had to deal with this that is going through this now. Because it is hard. It is so hard.”

At least two other people were wounded: David Dutch, 57, of New Kensington, Pennsylvania, and James Copenhaver, 74, of Moon Township, Pennsylvania, both towns outside Pittsburgh. Each man was listed in stable condition Sunday.

Monteleone, who wore the “Trump 2024” denim vest that her husband made, said the ordeal and Trump’s fist pumps only made her “more MAGA, more pro-America than ever.”

“We were not scared. We were angry,” Monteleone said. “And we will not surrender. We will vote for him. We will support him. He is a strong leader, and that’s what America needs.”

As Trump was spirited away, many rally-goers directed that anger toward the journalists documenting the rally, shouting obscenities and extending their middle fingers. “Are you happy?” some yelled.

And Sweetland? A day afer the shooting, his shock had turned to anger.

“I just hope and pray everybody takes a step back, a deep breath, lowers their temperature and stops all this vitriolic comments that are being made,” he said. “This is not the United States I know and love, and I love this country dearly.”

More coverage In a world of moving pictures, photographs capture indelible moments in Trump assassination attempt How the attempted assassination of former President Trump unfolded Former fire chief who died at Trump rally used his body to shield family from gunfire

WATCH: AP photographer Evan Vucci describes the moment when shots were fired

Associated Press photojournalist Evan Vucci has covered former President Donald Trump for years, but what occurred on Saturday in Butler, Pennsylvania was a time stopping moment in history, and Vucci recounts his experience from the rally with Trump.

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Associated Press reporters Carolyn Thompson, Stefanie Dazio, Colleen Long and Brian Slodysko contributed to this report.