The FBI named 20-year-old Thomas Matthew Crooks of Bethel Park, Pa., as the suspected shooter in what it described as an assassination attempt on former president Donald Trump at a rally in Butler, Pa., on Saturday.

The Secret Service said its agents "neutralized" the shooter, who is now dead. Trump said in a post on Truth Social that he was "shot with a bullet that pierced the upper part of my right ear." One spectator was killed, and two others were critically injured.

Relatively little is publicly known about Crooks, though in the coming hours and days, his background and possible motives will be the subject of intense focus by media and law enforcement. Here's what we know.

Who was Thomas Matthew Crooks?

Crooks was 20 years old and from Bethel Park, Pa. - about 40 miles south of Butler, the location of Saturday night's Trump rally, the FBI said.

A local media outlet's list of graduates of Bethel Park High School in 2022 listed Thomas Crooks as one of 20 students to have received a $500 prize for math and science from the school that year. Bethel Park High School did not immediately reply to a request early Sunday for comment.

Crooks was registered as a Republican, according to Pennsylvania's voter status records.

By early Sunday, authorities had sealed off the area around the alleged shooter's home. Local fire department vehicles blocked access for several blocks, allowing only residents and investigators to enter.

What do we know about the investigation?

The suspected shooter used an AR-15-style semiautomatic rifle to carry out the attack, a U.S. official and another person familiar with the investigation said, speaking on the condition of anonymity to discuss a probe that is still in its early stages.

When the FBI named Crooks as the suspect, the bureau said this "remains an active and ongoing investigation" and urged anyone with relevant information to submit it to the agency.

In a news conference Saturday evening, before the alleged shooter was named, FBI Pittsburgh Special Agent in Charge Kevin Rojek said the agency did not yet know his motivation. "Our investigators are working tirelessly to attempt to identify what that motive was," he said.

Pennsylvania State Police Lt. Col. George Bivens was asked whether the shooter acted alone and responded that it was "too early to say that."

"It will be some time until we can conclusively ... answer that question," he added.

Bivens described a "chaotic" scene at the rally after shots were fired in the direction of Trump as he was speaking on the rally stage. He said federal and local agencies were working together to interview witnesses and process the crime scene.

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