BUTLER, Pa. — On the heels of an attempt to kill him, former President Donald Trump called Sunday for unity and resilience as shocked leaders across the political divide recoiled from the shooting that left him wounded but ”fine.”

A former fire chief attending the rally with family was killed, as was the gunman. Two other people were also critically wounded.

The presumptive Republican presidential nominee said the upper part of his right ear was pierced in the shooting. His aides said he was in ”great spirits” and doing well.

”I knew immediately that something was wrong in that I heard a whizzing sound, shots, and immediately felt the bullet ripping through the skin,” he wrote on his social media site. ”Much bleeding took place.”

In a subsequent social post Sunday, Trump said ”it was God alone who prevented the unthinkable from happening.”

”In this moment, it is more important than ever that we stand United, and show our True Character as Americans, remaining Strong and Determined, and not allowing Evil to Win,” his post said.

Pennsylvania Gov. Josh Shapiro on Sunday identified the rallygoer who was killed as Corey Comperatore, a former fire chief from the area, and said he ”died a hero.”

”His wife shared with me that he dove on his family to protect them,” Shapiro said. He declined to discuss the condition of two others who were wounded.

The FBI identified the shooter as Thomas Matthew Crooks, 20, of Bethel Park, Pennsylvania, which is about 50 miles (80 kilometers) from the scene of the shooting. An FBI official said investigators had not yet determined a motive.

Secret Service agents fatally shot Crooks. The gunman attacked from an elevated position outside the rally venue at a farm show in Butler, the agency said.

Not long before shots rang out, rallygoers noticed a man climbing to the roof of a nearby building and warned local police, according to two law enforcement officials.

One local police officer climbed to the roof and encountered Crooks, who pointed his rifle at the officer. The officer retreated down the ladder, and Crooks quickly took a shot toward Trump, and that’s when Secret Service snipers shot him, said the officials, who spoke to The Associated Press on condition of anonymity to discuss an ongoing investigation.

The officials also told AP that bomb-making materials were found inside Crooks’ vehicle, and bomb-making materials were found at his home.

Investigators believe the weapon Crooks used was purchased by his father at least six months ago, the law enforcement officials said. Federal agents were still working to understand when and how his son obtained the gun and to gather additional information about Crooks, according to the officials.

Crooks’ political leanings were not immediately clear. Records show Crooks was registered as a Republican voter in Pennsylvania, but federal campaign finance reports also show he gave $15 to a progressive political action committee on Jan. 20, 2021, the day President Joe Biden was sworn in to office.

Authorities told reporters that Crooks was not carrying identification so they were using DNA and other methods to confirm his identity. Law enforcement recovered an AR-style rifle at the scene, according to a person familiar with the matter who spoke on condition of anonymity to discuss the investigation.

Most serious assassination attempt since 1981

The attack was the most serious attempt to kill a president or presidential candidate since Ronald Reagan was shot in 1981. It drew new attention to concerns about political violence in a deeply polarized U.S. less than four months before the presidential election. And it could alter the tenor and security posture at the Republican National Convention, which begins Monday in Milwaukee.

Trump said he will travel to Milwaukee for the GOP convention on Sunday afternoon, and organizers have said the convention will proceed as planned.

Trump flew to New Jersey after visiting a local Pennsylvania hospital, landing shortly after midnight at Newark Liberty International Airport. Video posted by an aide showed the former president leaving his private jet flanked by Secret Service agents and heavily armed members of the agency’s counterassault team, an unusually visible show of force by his protective detail.

Biden, who is running against Trump, said the two men had a ”short but good” conversation Saturday night. Biden cut short a weekend at his beach home in Rehobeth Beach, Delaware, to return to Washington, where he said during an address Sunday afternoon that ”there is no place in America for this kind of violence.”

”We cannot allow this to happen,” Biden said, adding that he ordered an independent review of security at the rally. Biden said he would speak again Sunday night from the Oval Office.

Many Republicans quickly blamed the violence on Biden and his allies, arguing that sustained attacks on Trump as a threat to democracy have created a toxic environment. They pointed in particular to a comment Biden made to donors on July 8, saying ”it’s time to put Trump in the bullseye.”

Officials said the counterassault team killed the shooter. The heavily armed tactical team travels everywhere with the president and major party nominees and is meant to confront any active threats while other Secret Service agents focus on safeguarding and evacuating the person at the center of protection.

An AP analysis of more than a dozen videos and photos from the scene of the Trump rally, as well as satellite imagery of the site, shows the shooter was able to get astonishingly close to the stage where the former president was speaking.

A video posted to social media and geolocated by the AP shows the body of a person lying motionless on the roof of a building at AGR International, a manufacturing plant just north of the Butler Farm Show grounds where Trump’s rally was held.

The roof where the person lay was less than 150 meters (164 yards) from where Trump was speaking, a distance from which a decent marksman could reasonably hit a human-sized target. For reference, 150 meters is a distance at which U.S. Army recruits must hit a scaled human-sized silhouette to qualify with the M-16 rifle. The AR-15, like the shooter at the Trump rally had, is the semi-automatic civilian version of the military M-16.

The range from which Crooks fired and his clothing led to early speculation that the shooter had military experience. However, all the branches of the military searched their records Sunday and said in response to a query by the AP that they had no records of him serving.

Asked at a news conference whether law enforcement did not know the shooter was on the roof until he began firing, Kevin Rojek, the agent in charge of the FBI’s Pittsburgh field office, responded that ”that is our assessment at this time.”

”It is surprising” that the gunman was able to open fire on the stage before the Secret Service killed him, he added.

Homeland Security Secretary Alejandro Mayorkas, whose department oversees the Secret Service, said officials were engaged with the Biden and Trump campaigns and ”taking every possible measure to ensure their safety and security.”

A rally disrupted by gunfire

Trump was showing off a chart of border crossing numbers when the gunfire began after 6:10 p.m.

As the first pop rang out, Trump said ”Oh” and raised his hand to his right ear and looked at it, before quickly crouching to the ground behind his lectern. The people in the stands behind him also crouched as screams rang through the crowd.

Someone could be heard near the microphone saying, ”Get down, get down, get down, get down!” as agents rushed to the stage. They piled atop the former president to shield him with their bodies as other agents took up positions on stage to search for the threat.

Afterward, voices were heard saying, ”Shooter’s down” several times, before someone asked, ”Are we good to move?” and ”Are we clear?” Then someone ordered, ”Let’s move.”

Trump could be heard on the video saying at least twice, ”Let me get my shoes,” with another voice heard saying, ”I’ve got you, sir.”

Trump got to his feet moments later and could be seen reaching with his right hand toward his face, which was streaked with blood. He then pumped his fist in the air and appeared to mouth the word ”fight” twice to his crowd of supporters, prompting loud cheers and then chants of ”USA. USA. USA.”

His motorcade left the venue moments later. Video showed Trump turning back to the crowd and raising a fist right before he was put into a vehicle.

In a statement Sunday, former first lady Melania Trump said that when she saw her husband wounded, ”I realized my life, and Barron’s life, were on the brink of devastating change,” referring to their son. She said she was grateful to Secret Service agents and other law enforcement officers, and offered her ”sincerest sympathy” to the families of the other victims.

Witnesses heard multiple gunshots and ducked for cover

When the firing began, ”everybody went to their knees or their prone position, because we all knew. Everyone becoming aware of the fact this was gunfire,” said Dave McCormick, the Republican candidate for U.S. Senate in Pennsylvania, who was sitting to Trump’s right on stage.

As he saw Trump raise his fist, McCormick said, he looked over his shoulder and noticed someone had been hit while sitting in the bleachers behind the stage.

Eventually, first responders were able to carry the wounded person out of a large crowd so he could get medical care, McCormick said.

Reporters covering the rally heard five or six shots ring out and many ducked for cover, hiding under tables. After the first two or three bangs, people in the crowd looked startled, but not panicked. An AP reporter at the scene reported the noise sounded like firecrackers at first or perhaps a car backfiring.

When it was clear the situation had been contained and Trump would not return to speak, attendees started filing out of the venue.

Police soon told the people remaining to leave the venue and Secret Service agents told reporters to get ”out now. This is a live crime scene.”

Political violence again shakes America

The perils of campaigning took on a new urgency after the assassination of Robert F. Kennedy in California in 1968, and again in 1972 when Arthur Bremer shot and seriously hurt George Wallace, who was running as an independent on a campaign platform that has sometimes been compared to Trump’s. That led to increased protection of candidates, even as the threats persisted, notably against Jesse Jackson in 1988 and Barack Obama in 2008.

Presidents, particularly after the assassination of John F. Kennedy in 1963, have even greater layers of security, and Trump is a rarity as both a former president and a current candidate.

Republican Rep. Mike Kelly, who represents the area where the shooting occurred, attended the rally with his wife and grandchildren and was just behind Trump when he was wounded. Kelly said he was ”in a state of bewilderment of how and what has happened to the United States of America.”

”I just wish people — tone it down,” he said. ”Quit trying to find, to blame somebody. The blame lies somewhere in the psyche of America.”

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Colvin, Balsamo and Price reported from New York. Long reported from Washington. Tucker reported from Westport, Connecticut. Associated Press writers Will Weissert, Michael Biesecker, Alanna Durkin Richer, Lisa Mascaro and Tara Copp in Washington, and Marc Levy in Harrisburg, Pennsylvania, contributed to this report.