VTA employee Kirk Bertolet, who saw the shootings and saw co-workers take their last breaths, said that Cassidy “made sure” his targets were dead.

“He was angry, and he took his vengeance out on very specific people. He shot people. He let others live,” he said. “It was very personal. Very targeted.”

Santa Clara County Sheriff Laurie Smith concurred that Cassidy’s victims seemed chosen, and that the gunman had told one or more people that he wasn’t going to shoot them. Although Bertolet described a cordial personal dynamic with Cassidy, he also characterized the 57-year old as an outsider in the workplace who never spoke to his colleagues.

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

Cassidy’s ex-wife, Cecilia Nelms, told AP that he would often return home from work angry and had even spoken about killing fellow employees.

“I never believed him, and it never happened. Until now,” she said.

For more reporting from the Associated Press, see below.

Authorities have not speculated on a motive beyond characterizing Cassidy on Thursday as a “highly disgruntled VTA employee for many years, which may have contributed to why he targeted VTA employees.”

Glenn Hendricks, chair of the VTA’s Board of Directors, said Thursday that he had no information about any tensions between Cassidy and the co-workers he shot.

“VTA is a close family,” Hendricks said. “I would let the investigation work itself out.”

The investigation is complicated. It spans two crime scenes—Cassidy apparently had a device that would set his home on fire almost simultaneously to when he began shooting—and has 100 potential witnesses who were working at the railyard at the time.

Cassidy arrived at the rail yard around 6 a.m., carrying a duffel bag containing three semi-automatic handguns and 32 high-capacity magazines. It’s not clear exactly when the bloodshed began, but the first 911 call reporting an active shooter came at 6:34 a.m.

“We were sitting in the front of our office and we started hearing the pops,” Bertolet said. “BANG. BANG. BANG, BANG, BANG.”

He and his co-workers threw a table in front of the door as Bertolet called the facility’s control center while the shooting continued.

The gunshots caused Rochelle Hawkins, a VTA mechanic, to drop her cellphone in the tumult.

“I was running so fast, I just ran for my life,” she said.

One of the victims, Taptejdeep Singh, tried to save his friend before Cassidy turned the guns on him.

“Taptejdeep called me to warn me that there was an active shooter in Building B and to go hide or get out immediately,” Sukhvir Singh said.

Sukhvir Singh survived. His friend did not.