(AP) The 20-year-old man who tried to assassinate former President Donald Trump first came to law enforcement’s attention at Saturday’s rally when spectators noticed him acting strangely outside the campaign event. The tip sparked a frantic search, but officers were unable to find him before he managed to get on a roof, where he opened fire.

In the wake of the shooting that killed one spectator, investigators are hunting for any clues about what may have drove Thomas Matthew Crooks, of Bethel Park, to carry out the shocking attack.

The FBI said they were investigating it as a potential act of domestic terrorism, but the absence of a clear ideological motive by the man shot dead by Secret Service allowed conspiracy theories to flourish.

The FBI said it believes Crooks, who had bomb-making materials in the car he drove to the rally, acted alone. Investigators have found no threatening comments on social media accounts or ideological positions that could help explain what led him to target Trump.

Crooks graduated from Bethel Park High School in 2022. His senior year, Crooks was among several students given an award for math and science, according to a Tribune-Review story at the time.

He tried out for the school’s rifle team but was turned away because he was a bad shooter, said Frederick Mach, a current captain of the team who was a few years behind Crooks at the school.

Jason Kohler, who said he attended the same high school but did not share any classes with Crooks, said Crooks was bullied at school and sat alone at lunch time. Other students mocked him for the clothes he wore, which included hunting outfits, Kohler said.