FBI searches for motive in Trump assassination attempt, cautions that investigation is still 'early'

BUTLER, Pa. — Much about the man who allegedly took aim at a former president on Saturday remained a mystery on Monday, as teams of FBI investigators scoured the 20-year-old's gunman's background, building a timeline of his actions and sifting through his digital history in search of a motive.

The attempted assassination was being investigated as a potential act of domestic terrorism, the FBI said in a statement late Sunday.

"The FBI has not identified a motive for the shooter’s actions, but we are working to determine the sequence of events and the shooter’s movements prior to the shooting, collecting and reviewing evidence, conducting interviews, and following up on all leads," the bureau said in the statement.

Trump was shot in an assassination attempt at an election rally in Butler, Pennsylvania, on Saturday, the FBI said. Secret Service agents swarmed the former president before leading him off the stage to a waiting vehicle. Trump is "fine," a spokesperson later said.

The alleged shooter, Thomas Matthew Crooks, was shot and killed at the scene, the Secret Service said. One spectator was killed and two were hurt, officials said.

Investigators have begun retracing the suspect's steps, an attempt to figure out how Crooks could have made it up onto the roof, which had been swept prior to the event, law enforcement sources told ABC News.

He was perched on the building outside the security perimeter, where the crowd passing through was checked for weapons, but was fewer than 400 feet from the podium where Trump was speaking, officials said.

FBI investigators, led by the Pittsburgh Field Office, have searched Crook's home in Bethel Park, a suburb of Pittsburgh. They've also searched his vehicle, which was at the scene of the shooting in Butler, the FBI said.

"Suspicious devices found at both locations have been rendered safe by bomb technicians and are being evaluated at the FBI Laboratory," the FBI said.

The AR-15 style rifle allegedly used by Crooks had been legally purchased by the suspect's father, law enforcement sources told ABC News. The family is cooperating with the investigation.

The bureau said it has also began combing through the shooter's phone.

"At present, we have not identified an ideology associated with the subject," Kevin Rojeck, a special agent, said. "But I want to remind everyone that we're still very early in this investigation."

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