A retired doctor recounts his attempt to save a wounded man who protected his wife and daughter during a Trump rally.

At a campaign event for former President Trump, a volunteer firefighter was killed by the gunman while a attendee stepped up to help the wounded.

Dr. James Sweetland, a retired emergency physician, recounted the horrific events on "Planet Chronicle @ Night," stating that the shots sounded like firecrackers at first.

He stated that there were three pops, a brief pause of about three or four seconds, and then four more pops.

"As everyone in the bleachers turned to look over the field and a line of trees, I saw where it was coming from. Then, I turned back to see Secret Service agents piling on President Trump, forming a human pyramid of about six agents."

The doctor then heard a woman scream for help nearby in the bleachers.

"A woman from the stands, 30 feet away to my right and down on the benches, shouted that a man had been shot and was calling for help."

Dr. Sweetland then rushed over to help 50-year-old Corey Comperatore.

As I approached him, I saw people crouched down and a pool of blood. Unfortunately, there was brain matter mixed in. I quickly examined him and found a bullet wound just above his right ear. It appeared to be fatal.

Dr. Sweetland performed CPR on Comperatore but declared that he had no pulse and was not breathing.

"I remember the look of grief, apprehension, and hope on their faces when I looked up at them while performing CPR on my husband and daughter. Despite the shock and sadness, I found the strength to say, "He's being taken where he can get help.""

A 20-year-old man snuck onto a roof and started shooting at Trump during a rally in Butler, Pennsylvania, and Comperatore shielded his wife and family from the gunfire.

Two rally-goers were injured in the shooting that also narrowly missed Trump, who sustained a minor hit to the ear.

The two other victims have been identified as James Copenhaver, 74, of Moon Township, Pa., and David Dutch, 57, of New Kensington, Pa., by law enforcement.

As the gunfire erupted, Trump fell to the ground, enveloped by Secret Service personnel. At first, it was uncertain if he had been struck.

"I assumed there was something going on behind me," Dr. Sweetland said, "because I heard a roar from the crowd behind me and didn't turn around."

"I didn't realize until later that the cheers were in response to his fist bump in the air, which the crowd was hoping to indicate that he was okay."

Despite the tragedy, the former president still plans to attend the Republican National Convention in Milwaukee. Trump has revised his speech after a shooter tried to kill him on Saturday, and will now focus on unity.

The ongoing investigation into the assassination attempt is being led by the FBI, with the shooter being identified as Thomas Matthew Crooks, 20.

This report was contributed to by Brooke Singman, Greg Norman, Michael Ruiz, Lucas Tomlinson, Sarah Rumpf-Whitten, Anders Hagstrom, Gabriele Regalbuto, Michael Lee, Greg Wehner, Bradford Betz, Stepheny Price, Louis Casiano, Landon Mion, and Elizabeth Pritchett.