The Federal Bureau of Investigation (FBI) has identified Thomas Matthew Crooks as the shooter behind the attempted assassination of former US President Donald Trump, it said in a statement on Sunday.

Crooks, 20, was killed by security officials when he opened fire at the 78-year-old Republican presidential candidate, injuring his right ear, during a campaign rally in Butler, Pennsylvania. 

“The FBI has identified Thomas Matthew Crooks, 20, of Bethel Park, Pennsylvania, as the subject involved in the assassination attempt of former President Donald Trump on July 13, in Butler, Pennsylvania,” the FBI said in a statement quoted by NBC and CBS.

Law enforcement officials earlier told reporters they had tentatively identified the suspected shooter but were not ready to do so publicly. They also said they had not yet identified the motive.

The FBI, which is the lead federal law enforcement agency in the investigation, had said the shooting was being treated as “an assassination attempt” against the former president.

Trump was rushed off stage with blood streaked across his face after the shooting, which left a bystander dead and two others critically injured.

He had just started speaking at his final rally before the Republican National Convention when multiple bangs ran out. He was bundled away to safety, and said afterward, “I was shot with a bullet that pierced the upper part of my right ear.”

The shocking incident occurred less than four months before the November 5 US presidential election, when Trump is set to face an election rematch with Democratic President Joe Biden.