Federal investigators are examining the possibility that a would-be assassin scoped out the area where former President Donald J. Trump was to speak six days before the campaign rally in Pennsylvania where Mr. Trump was wounded.
A cellphone linked to the gunman, Thomas Matthew Crooks, 20, of Bethel Park, Pa., included geolocation data that indicated that he could have been in the area of the site, the Butler Farm Show grounds, on July 7, according to federal officials and information provided by the F.B.I. on Wednesday during a congressional briefing. Mr. Crooks opened fire from a warehouse roof at the site on Saturday, grazing the former president’s right ear, killing a rally attendee and seriously injuring two others.
The new details about Mr. Crooks’s possible whereabouts on July 7 mean that he might have checked out the site even before law enforcement officials did a security assessment. The Secret Service met with local law enforcement officers for a first walk-through on July 8, and finalized plans a few days later.
The Secret Service ultimately decided to exclude from the security zone a complex of warehouses to the north of Mr. Trump’s stage, despite the closest one being within a rifle’s range. That decision is now under intense scrutiny by Congress. The F.B.I. is responsible for investigating the attempted assassination, but officials have not said whether the bureau intends to write a report.
Federal officials, speaking on the condition of anonymity to discuss details about the ongoing inquiry, said the F.B.I. had learned more about Mr. Crooks’s movements after he might have surveilled the show grounds.
He told his employer at the nursing home where he worked that he needed to take Saturday off because he had to do something important.
Then, on the afternoon before the shooting, Mr. Crook visited a gun range, officials said. The next morning, he bought a ladder at a Home Depot — though officials do not believe he ended up using any ladder to ascend to the warehouse roof — and then purchased ammunition at a nearby gun store, Allegheny Arms and Gun Works.
After Secret Service snipers killed Mr. Crooks, the authorities recovered a bulletproof vest and several magazines for the rifle from his car, along with rudimentary explosive devices.
The F.B.I. continues to examine cellphones, laptops and thumb drives that belonged to Mr. Crooks, hoping to glean clues about what drove him to shoot the former president. The F.B.I. is intensely focused on developing a portrait of Mr. Crooks and what he did during the last months of his life.
Typically, the F.B.I. is able to gather an enormous amount of information within days about shooters in high-profile investigations, but for the most part Mr. Crooks has remained an enigma, leaving few clues online.
The F.B.I. has said that Mr. Crooks did not suffer from any known mental illness, but in the briefing to Congress, officials said he had searched online for “major depressive disorder.”