Before he climbed onto a rooftop and added his name to America’s bloody history of would-be presidential assassins, Thomas Crooks, 20, seemed to try to shrink from view.

Jim Knapp, who was the gunman’s guidance counsellor at Bethel Park High School in the suburbs south of Pittsburgh, said Crooks chose to sit by himself at lunch in the cafeteria and look at his phone, instead of joining other students.

”He just wanted to stay by himself,” Knapp said.

In interviews on Monday, former classmates had similar recollections.

They described Crooks as a smart but solitary student who walked through the halls with his head down and rarely raised his hand in class. But they said he did not make threats or act violently.

“He didn’t want attention, good or negative,” said Julianna Grooms, 19, who first remembered seeing Crooks when they were freshmen.

She and other former classmates have spent days texting one another, looking at old high-school photos and racking their memories for some clue about why Crooks opened fire at a Trump rally in Butler, Pennsylvania, on Saturday, killing one attendee, critically wounding two others and grazing former President Donald Trump in the ear. Crooks was shot and killed by the Secret Service.

On Monday, federal investigators did not provide any new answers about the gunman’s motives or ideology, but said they had been able to access to Crooks’ cellphone and were analysing it, along with his other electronic devices.