Five years before Samuel Cassidy opened fire at the San Jose light rail yard where he worked, killing eight of his-coworkers, border authorities discovered he owned “a black memo book filled with lots of notes about how he hates the VTA,” according to a Department of Homeland Security memo obtained by The Wall Street Journal. The Journal reports that in 2016, U.S. Customs officers detained Cassidy, 57, after a trip to the Philippines. During questioning, border agents found his book of notes about the Santa Clara Valley Transportation Authority. He also had “books about terrorism and fear and manifestos,” according to the memo. “When asked if he had problems with anybody at work, he stated ‘no,’” the memo says.

On Wednesday morning, Cassidy arrived at the VTA with three semi-automatic handguns and 11 loaded magazines and went on a shooting rampage. The Santa Clara County Sheriff’s Office said Thursday the attack was deliberate and that Cassidy seemed to have selected his targets, telling one employee “I’m not going to shoot you.” “And then he shot other people. So I imagine there was some kind of thought on who he wanted to shoot,” Sheriff Laurie Smith said. After the attack, Cassidy died by a self-inflicted gunshot wound.