WASHINGTON — The gunman in the assassination attempt on former President Donald Trump searched online for events of both Trump and President Joe Biden, looked up information about explosives over the last five years and eyed the Pennsylvania campaign rally where he opened fire last month as a “target of opportunity,” a senior FBI official said Wednesday.

Investigators who have conducted nearly 1,000 interviews do not yet have a motive for why 20-year-old Thomas Matthew Crooks shot at Trump during a July campaign rally but they believe that he conducted “extensive attack planning,” including looking up campaign events involving both the current president and former president, particularly in western Pennsylvania.

The FBI analysis of his online search history reveals a “sustained, detailed effort to plan an attack on some event, meaning he looked at any number of events or targets,” Kevin Rojek, the special agent in charge of the FBI’s Pittsburgh field office, told reporters Wednesday in the latest in a series of briefings on the investigation.

Once a Trump rally was announced for July 13 in Butler, Pennsylvania, “He became hyper-focused on that specific event and looked at it as a target of opportunity,” Rojek said. Crooks’ internet searches in the days leading up to the rally included queries about the grounds where the rally was held, “Where will Trump speak from at Butler Farm Show?” “Butler Farm Show podium” and “Butler Farm Show photos.”

In the 30 days before the attack, the FBI says, Crooks did more than 60 internet searches related to Biden and Trump, including seeking the dates of both the Democratic and Republican national conventions. FBI Director Christopher Wray has previously revealed that one week before the shooting, Crooks did a Google search for “How far away was Oswald from Kennedy?”

That’s a reference to Lee Harvey Oswald, the shooter who killed President John F. Kennedy on Nov. 22, 1963.

The new details add to an emerging portrait of Crooks as a highly intelligent and reclusive man who investigators say in the years before the shooting had taken an interest in explosives, violence and prominent public figures but whose internet searches of Democrats and Republicans alike have frustrated efforts to assign a simple political motive or to establish why Trump himself would have been targeted.

“We have a clear idea of mindset, but we are not ready to make any conclusive statements regarding motive at this time,” Rojek said.

The FBI has also not found that anyone else had advance knowledge of the shooting or that Crooks had conspired with anyone else.

The FBI found explosive devices in his car and home, and investigators say his internet searches revealed that since at least 2019 he had looked up information about bomb-making materials, including about how remote detonators work.

The FBI has said that Trump, the 2024 Republican presidential nominee, was struck in the ear by a bullet or a bullet fragment in the assassination attempt. Crooks fired eight shots from an AR-style rifle. One rallygoer was killed and two others were injured before the gunman, who was positioned on the roof of a building less than 150 yards away, was killed by a Secret Service counter-sniper.

Also Wednesday, the FBI released images of the rifle Crooks used, his backpack and improvised explosive devices found in his car.