The FBI said Monday that agents have accessed the data on the cellphone belonging to Crooks but are still trying to determine why he opened fire at a Saturday rally for Trump in Butler, Pa., wounding the former president and leaving one rallygoer dead and two others critically injured. Technical experts “successfully gained access to Thomas Matthew Crooks’ phone, and they continue to analyze his electronic devices,” the agency said in a statement.

Even with access to the gunman’s phone, family and friends, investigators have found little information pointing to the gunman’s motive, according to people familiar with the investigation who spoke on the condition of anonymity to discuss an ongoing investigation. FBI officials have said they do not have meaningful evidence of an ideology driving him to commit the act. In talking to everyone he knew, and examining the phones of some of the people he communicated with, investigators are still trying to understand why he would carry out such an attack.

President Biden and Vice President Harris were briefed Monday morning in the Situation Room by senior law enforcement and security officials, including FBI Director Christopher A. Wray, Attorney General Merrick Garland and Homeland Security Secretary Alejandro Mayorkas.

Secret Service Director Kimberly Cheatle also participated, as her agency faces questions over how Crooks managed to get on the roof of a building outside the rally’s security perimeter and open fire. Video taken just before the attack appears to show some spectators trying to alert police to the shooter’s presence.

Crooks, of Bethel Park, Pa., graduated in May with an associate’s degree in engineering science from the Community College of Allegheny County in western Pennsylvania, according to a college spokesperson.

“Like all Americans, we are shocked and saddened by the horrific turn of events that took place in Butler, Pa., on Saturday,” the community college said in a statement. It expressed relief that Trump is safe and offered condolences to the family of Corey Comperatore, the 50-year-old engineer and father of two who was killed.

Crooks planned to enroll at Robert Morris University this fall, according to a university spokesperson. He also worked at a local nursing home.

At the community college, Crooks was a part of a proof-based mathematics book club that met weekly, according to a former classmate who spoke on the condition of anonymity to protect his privacy. While Crooks was interested in math, the classmate said he took more of a liking to physics.

The classmate said Crooks was a reserved person, rarely talking about politics at school and politically leaning more moderate to central right. When the classmate heard Crooks identified as the gunman, he texted Crooks saying he was sorry someone was trying to impersonate him. He didn’t receive a text back. Then, his classmate saw the photo of Crooks fatally shot on the roof of a building.

“If I had to speculate, I would assume this was a suicide-by-cop,” said the classmate, who considered Crooks a friend. “Tom was a good guy, I assumed he was going to live a good life. I don’t know what drove him to do this. I worry about our democracy, his family, the Crooks. I feel awful for the firefighter’s family.”

Police and volunteer firefighters had the gunman’s entire neighborhood blocked off Sunday, but the area was reopened to the public Monday. Crooks lived in a small, one-story brick home.

Liam Campbell, who lives across street, said he and his family were rustled out of bed around midnight Saturday by police who were evacuating the neighborhood for fear that there might be an explosive device inside Crooks’s house.

“They said there was a device in a neighboring household that needed to be removed and that just we need to get everyone out of the house out and stay somewhere,” said Campbell, 17, adding that he was not allowed to return home until 10 p.m. Sunday.

During Campbell’s freshman year of high school, he and Crooks rode the school bus together. But Campbell said Crooks “kept to himself” and didn’t seem to interact with many people at school or in the neighborhood.

“He would just walk around the neighborhood by himself,” Campbell said. “He was a quiet kid and he was kind of strange. He sat by himself. Didn’t talk to anyone. … But he just seemed like a normal person who just didn’t like talking to people.”

FBI special agent in charge Kevin Rojek said Crooks used an AR-style rifle chambered in 5.56mm, a common caliber for such weapons. Authorities said the weapon was identified and traced using records from a gun dealership that is no longer operating.

On the morning of the shooting, the person familiar with the investigation said Crooks bought 50 rounds of ammunition at a local gun store called Alleghany Arms. The store owner and employees declined to comment when visited by a reporter from The Washington Post on Monday morning, offering a statement that said they have a “prerogative to cooperate with law enforcement in every way.”

“We are thankful that President Trump was not assassinated and our hearts and prayers go out to all victims of this horrible incident,” the statement said.

The gunman was a member of the Clairton Sportsmen’s Club, a shooting club in Clairton, Pa., a club lawyer confirmed Monday.

The club “fully admonishes the senseless act of violence that occurred on Saturday,” Robert S. Bootay III said. He added that the club “offers its sincerest condolences to the Comperatore family and extends prayers to all of those injured, including the former president.”

Barrett and Hilton reported from Washington. Alice Crites, Monika Mathur, Razzan Nakhlawi, María Luisa Paúl, Aaron Schaffer, Perry Stein and Matt Viser in Washington contributed to this report.