Of course, it is coming to light that the man who killed nine of his coworkers before taking his own life had been recently reported for making racist comments at work.

Sam Cassidy was facing a disciplinary hearing at the Valley Transportation Authority on Wednesday, the same day that he brought three semi-automatic pistols with him to work with the intent to kill multiple people. As NBC Bay Area reports, Cassidy had been the subject of recent complaints from coworkers about "making inappropriate racial remarks to colleagues."

It remains unclear whether this was directly tied to his motive in the shooting.

At least 50 FBI agents have been on the case, combing both the scene at the VTA maintenance yard where the shooting took place, and at Cassidy's home on Angmar Court, about eight miles away. An incendiary device or devices caused the home to catch fire Wednesday morning nearly simultaneously with the shooting, and firefighters reported ongoing explosions or bursts of flames throughout the morning and day. Explosives and ammunition were found at the home — and reportedly agents have recovered 32 high-capacity, 12-round magazines for semi-automatic weapons.

Authorities are also just learning about a run-in that Cassidy had with Homeland Security on his way back into the country from a trip to the Philippines in 2016. As the Wall Street Journal reports, U.S. Customs and Border Protection agents questioned Cassidy after finding "books about terrorism and fear and manifestos…as well as a black memo book filled with lots of notes about how he hates the VTA" in his possession. It remains unclear why agents stopped him or went through his bags.

Border agents apparently asked Cassidy whether he "had problems with anybody at work," according to a memo about the incident, and he said, "No."

But clearly Cassidy had been a disgruntled employee whose issues with his workplace went back two decades, according to his ex-wife.

It does not seem as though information about Cassidy's notebook was shared with the VTA after the 2016 incident. FBI Special Agent in Charge of the San Francisco division, Craig Fair, tells KTVU that if there was "threat to life information, either self-harm or threat to others" in his notebook, that would have had to have been shared with local authorities.

Fair said further that there were likely overt signs or behaviors that Cassidy was ramping up to a violent act.

"Generally people just don’t snap," Fair said in comments on Thursday to the Chronicle. "There’s a mobilization phase. There’s a ramp-up, to the point where they actualize their plans. But during that ramp-up phase, there’s leakage. They’re projecting something, and it’s overt and is visible to the public, family and friends, educators, law enforcement and/or mental health officials. That’s the case with nearly all of these folks."

In a new interview with the Associated Press, a survivor of the shooting and a coworker of Cassidy, Kirk Bertolet, describes Cassidy as a "loner" and an "outsider" who "never fit in" at the VTA.

"I understand what pushed him," Bertolet said. "Sam was always on the outside. He was never in the group. He was never accepted by anybody. You look back and you go, ‘yeah, it fits.’ ”

Related: These Are the Nine VTA Employees Killed In Wednesday's Shooting In San Jose