SAN JOSE (CBS SF/AP) — Kirk Bertolet huddled inside his office as the horror of Wednesday’s mass shooting at the Santa Clara Valley Transportation Authority unfolded. Once the gunfire and screams stopped, he carefully raced out to see if he could help the victims.

The 64-year-old is a VTA signal maintenance worker and who worked in a separate unit from gunman Samuel Cassidy. He firmly believes that Cassidy targeted his nine victims.

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“He was pissed off at certain people. He was angry, and he took his vengeance out on very specific people. He shot people. He let others live,” he told the Associated Press. “It was very personal.”

Santa Clara County Sheriff Laurie Smith also believes that some or all of the victims were targeted.

“It appears to us at this point that he said to one of the people there: ‘I’m not going to shoot you,’” Smith said. “And then he shot other people. So I imagine there was some kind of thought on who he wanted to shoot.”

On Thursday, Smith’s department issued a news release calling the gunman a “highly disgruntled VTA employee for many years.”

Jeff Harp, former assistant special agent in charge of the San Francisco FBI office, told KPIX 5 that Cassidy had to know there would be a quick response nearby law enforcement once he began opening fire. He was armed with three automatic handguns and had illegal magazines loaded with ammunition.

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“He was certainly aware that VTA was in close proximity to the sheriff’s department,” Harp told KPIX 5. “He knew that. He’d worked there for years. He knew it was going to happen quick.”

Still a video released Thursday night showed the gunman casually walking between the two buildings where he opened fire on the employees.

He fired 39 bullets before killing himself as police officers and sheriff’s deputies closed in.

Cassidy’s ex-wife said he had talked about killing people at work more than a decade ago. Cecilia Nelms told The Associated Press that he used to come home from work resentful and angry over what he perceived as unfair assignments.

Federal authorities authorities said that Cassidy had been detained by U.S. Customs agents five years ago because he had writings about terrorism and hating his workplace.

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Those who died have been identified as:

  • Paul Delacruz Megia, age 42
  • Taptejdeep Singh, age 42
  • Adrian Balleza, age 29
  • Jose Dejesus Hernandez III, age 35
  • Timothy Michael Romo, age 49
  • Michael Joseph Rudometkin, age 40
  • Abdolvahab Alaghmandan, age 63
  • Lars Kepler Lane, age 63
  • Alex Ward Fritch, age 49