An emergency room doctor attending former President Donald Trump's campaign rally in Pennsylvania told CBS News that he tried to help render aid to an audience member who was gravely wounded when a gunman opened fire on Saturday.

The gunman, identified as 20-year-old Thomas Matthew Crooks, fired several rounds while Trump was speaking at the rally in Butler, Pennsylvania, grazing the former president's ear. One rallygoer — identified Sunday as Corey Comperatore — was killed and two others were critically wounded, the FBI said. 

Dr. Jim Sweetland, who spoke to CBS News campaign reporter Jake Rosen right after the shooting, said when he heard the loud bangs, he first thought they were firecrackers before realizing they were gunshots.

"Somebody over there was screaming 'he's been shot, he's been shot,'" Sweetland told Rosen. "So I made my way over, I said 'I'm an emergency department physician, let me help you.'"

Sweetland said the victim had a gunshot wound to the head and had fallen between the bleachers. He told CBS News on Sunday that spectators helped him get the wounded man on a bench so that he could help render aid.

The victim had no pulse and was not breathing, Sweetland said, so he said he performed CPR and did chest compressions on the wounded man.

"There was lots of blood," he said, adding, "The people over there were really helpful."

He said he had rendered aid to the man for about two minutes before two Pennsylvania State Police officers arrived to take over.

"They picked him up, unfortunately like a ragdoll, and took him from the stands," Sweetland said, growing emotional. "I looked up to see his family who witnessed my efforts at resuscitation and the look on their faces said it all."

It was not immediately clear whether the badly wounded rallygoer the doctor was helping was Comperatore, the man who authorities said was killed at the event.

CBS News' Rosen spoke to other witnesses who were traumatized by the shooting.

"I spoke to a couple other people who were in the front row who were worried about the children who they say witnessed the shooting, children who were right next to the person who died," Rosen said. "And I spoke to a couple other older women who were right next to the person who died."

The FBI is leading the investigation into the shooting, and a motive has not yet been identified.

Two law enforcement sources told CBS News that the suspect was spotted outside the security perimeter as people were filing into the rally, and he was reported by a bystander to the Butler County Sheriff's Office. He was identified as a suspicious person by police, the sources said. 

The suspect fired 6-8 rounds using a semi-automatic AR-style, approximately 400 feet from the podium. 

Secret Service counter-sniper teams "had him" within seconds — the threat was neutralized almost immediately after shots were fired, the law enforcement sources said. 

Trump issued a new statement early, saying that he looks "forward to speaking to our Great Nation this week from Wisconsin." The Republican National Convention is set to kick off Monday in Milwaukee.

The White House said late Saturday that President Biden had spoken to Trump by phone.

Jake Rosen, Nicole Sganga, Pat Milton and Caroline Linton contributed to this report.

In:
• Pennsylvania
• Trump Rally

Stephen Smith

Stephen Smith is a managing editor for CBSNews.com based in New York. A Washington, D.C. native, Steve was previously an editorial producer for the Washington Post, and has also worked in Los Angeles, Boston and Tokyo.