The tragic victim of the Donald Trump rally shooting has been identified.

       Corey Comperatore, a retired fire chief from Pennsylvania, sadly lost his life after gunfire erupted while Trump was in the middle of his speech in Buttler.

       Other rally attendees tried to save the life of Comperatore in the bleachers, but tragically he passed away after being hit by a bullet.

       His sister wrote on Facebook: "The PA Trump Rally claimed the life of my brother, Corey Comperatore.

       "The hatred for one man took the life of the one man we loved the most. He was a hero who shielded his daughters.

       READ MORE: Trump's assassination attempt 'should shock free world', James Cleverly writes

       "His wife and girls just lived through the unthinkable and unimaginable. My baby brother just turned 50 and had so much life left to experience.

       "Hatred has no limits and love has no bounds. Pray for my sister-in-law, nieces, my mother, sister, me and his nieces and nephews as this feels like a terrible nightmare but we know it is our painful reality."

       An emergency room doctor at the rally revealed how he performed CPR on another attendee, who is presumed to be Comperatore.

       "I heard the shots. I thought it was firecrackers begin with. Somebody over there was screaming 'he's been shot he's been shot,'' said the man on CBS News.

       "So I made my way over. I said I'm an emergency department physician. Let me help you."

       Despite the physician's best attempts the man died at the scene.

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       Thomas Matthew Crooks, 20, has been identified as the shooter in the apparent assassination attempt of the former President at his campaign rally in Butler, Pennsylvania, on Saturday.

       Investigators were working Sunday to gather more information about Crooks, of Bethel Park, Pennsylvania, who opened fire at the rally before being killed by Secret Service - days before Trump was to accept the Republican nomination for a third time.

       Trump was seen with blood dripping down the side of his ear as he was rushed off stage by Secret Service agents but is "fine".