State voter records show that Mr Crooks was a registered Republican. The upcoming 5 November election would have been the first time he was old enough to vote in a presidential race.

He lived about an hour away from where the shooting took place in Butler. The Federal Aviation Administration said that it closed the airspace over Bethel Park for "special security reasons."

When Thomas Crooks was 17, he made a $15 donation to ActBlue, a political action committee that raises money for left-leaning and Democratic politicians, according to a 2021 Federal Election Commission filing.

The donation was earmarked for the Progressive Turnout Project, a national group that rallies Democrats to vote. The groups did not immediately respond to a Reuters request for comment.

Mr Crooks' father, Matthew, 53, told CNN that he was trying to figure out what happened and would wait until he spoke to law enforcement before speaking about his son.

Thomas Crooks graduated in 2022 from Bethel Park High School, according to the Pittsburgh Tribune-Review.

The newspaper reported that he received a $500 "star award" from the National Math and Science Initiative.

A 2022 graduation ceremony video cited by the New York Times shows Crooks receiving his high school diploma to some applause.

Video from that ceremony posted online shows Thomas Crooks with glasses in a black graduation gown and posing with a school official. Reuters could not immediately verify the authenticity of the video.

Law enforcement officials said that Crooks carried no identification to the site of the shooting and had to be identified using other methods.

"We're looking at photographs right now and we're trying to run his DNA and get biometric confirmation," Kevin Rojek, FBI special agent in charge, said during a press briefing.

USA Today reported that dozens of law enforcement vehicles were stationed outside a residence listed at the address on Crooks' voter registration record.