Steve Eder

Last July, a 20-year-old community college graduate opened fire at Donald J. Trump during a campaign rally in Butler, Pa., killing an attendee. As the months passed, questions persisted about how this quiet young man had become a killer. So we investigated.→

Tawnell D. Hobbs

In our reporting, we learned that Mr. Crooks’s mental health had been deteriorating. His father told investigators he would find him dancing at all hours of the night and talking to himself while waving his hands.

Steve Eder

At the same time, Mr. Crooks appeared to be living a fairly normal life. He worked and attended classes, excelling as an engineering student with plans for a career in aerospace or robotics. People who know him said they had no idea about his troubles.

Tawnell D. Hobbs

As we tried to understand Mr. Crooks’s downward path, we dug through government reports and public records about his academic life. In one essay we found, he argued for a voting method that would rank candidates by preference, saying the country needed a system that promoted kindness instead of division.

Steve Eder

Our reporting also took us to western Pennsylvania, where we talked to people who knew Mr. Crooks. Many people still did not want to talk; they were shaken by the events of the previous summer. Others said they were still searching to understand what happened.