Investigators Unlock Gunman’s Phone in Search of Motive for Trump Shooting

The motives of the young man who tried to assassinate former President Donald J. Trump remain a mystery, even after the F.B.I. gained access to his cellphone on Monday and began analyzing its contents for clues, law enforcement officials said.

Investigators hope the phone, which was password-protected, will help explain why Thomas Matthew Crooks, an unassuming 20-year-old from Pennsylvania with no criminal history or known strongly held political beliefs, would open fire at Mr. Trump at a rally on Saturday. The gunfire grazed the former president’s ear, killed a bystander and seriously injured two other people.

Technicians at the bureau’s lab in Quantico, Va., sifting through the gunman’s texts, emails and other data did not immediately find clear evidence of a potential motive, or significant new details about possible connections to other people.

The F.B.I., in a statement on Monday, cautioned that the investigation was still in the early stages. Technicians are in the middle of analyzing all of the gunman’s electronic devices, not just his phone, for his communications, browser history and social media activity, officials added.

As Mr. Trump’s attention shifted to the Republican National Convention in Milwaukee, dozens of agents and technical specialists in the Pittsburgh area scoured photos and videos taken by rally attendees and law enforcement personnel. The bureau has interviewed more than 100 people in the last two days, and completed a search of the gunman’s car and residence.

What they have assembled so far is less a portrait of him than an empty frame.

Records show that Mr. Crooks, a nursing home employee, registered to vote as a Republican. But people close to him have told investigators that he rarely spoke about