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SAN JOSE, Calif. - The Santa Clara County Sheriff's Office on Thursday continued its investigation in the deadliest mass shooting in Bay Area history.
Federal investigators are working with local law enforcement to collect evidence and recreate a 3-D version of the crime scene to get a better understanding of what unfolded early Wednesday morning.
So far, authorities have determined that around 6:30 a.m. 57-year-old Samuel James Cassidy was armed with 3 semi-automatic handguns and 32 high-capacity magazines during the attack.
Samuel James Cassidy
Cassidy, a disgruntled VTA employee, entered the light rail yard near North 1st and San Pedro and unleashed a hail of bullets. Sheriff's officials said he fired 39 rounds, ultimately killing nine people.
Investigators have not pinpointed an exact motive for the attack, but as more pieces fit together they have learned that Cassidy had hated his job for years.
The gunman was detained by federal border agents in 2016 with books about terrorism and a memo book of notes of how mich about how he hated his job, according to a Biden administration official who described a Department of Homeland Security memo detailing the encounter.
However, Bay Area law enforcement agencies weren't notified about the incident because it did not appear to pose any threat to life, according to the FBI Special Agent in Charge of the San Francisco division, Craig Fair.
SEE ALSO: Widow of slain VTA employee says her husband and 'rock' died in her arms
"If there was threat to life information, either self-harm or threat to others, the process is set up that it would typically trickle down [to local authorities}," Fair told KTVU on Thursday. "And again I have not seen the memo. And I don’t know if there was actual threat to life in that memorandum."
Kirk Bertolet, a VTA employee who survived the attack, told the Associated Press that Cassidy was an "outsider."
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Bertolet said he was barricaded in his office as shots rang out, but left to search for anyone who needed help. But all he found were bodies.
"There wasn’t helping anybody," the 64-year-old said, choking up. "He made sure they were all dead. I watched some of my coworkers breathe their last breath. And they were all gone."
Bertolet, who works in the signals department, said he had a polite relationship with Cassidy when they would pass in the locker room or hallway. He described "Sam" as an outsider at the facility, a loner who sat by himself, never talked to anyone and never fit in. He appeared to target specific coworkers, Bertolet said.
"I understand what pushed him. Sam was always on the outside. He was never in the group. He was never accepted by anybody," Bertolet said Thursday during an interview with The Associated Press. "You look back and you go, ‘yeah, it fits.’