A witness affirms that the aggressor chose who he would shoot in San José

"What the hell is wrong with us?" Says California Governor 4:53

(CNN) -

The attacker who opened fire on his co-workers at a light rail station in Northern California on Wednesday, killing nine people before committing suicide, left out certain people and therefore appeared to target the people. he shot, a witness said, 'He… was targeting certain people. He missed other people, "Kirk Bertolet, a worker at the Santa Clara Valley Transportation Authority (VTA) in San Jose, told CNN affiliate KGO Wednesday night. "He let some people live while shooting others to death."

The attacker, armed with two semiautomatic pistols, shot his co-workers in two buildings around the time of a morning shift change before taking his own life in front of responding police officers, authorities reported.

At least eight of the nine killed were VTA employees, and investigators are trying to determine why, according to authorities.

The shooting is the latest example of the scourge of gun violence in the United States.

It is the 232nd mass shooting, which CNN defines as a shooting in which at least four people are wounded or injured, so far this year, according to a tally by the Gun Violence Archive.

There were 17 such shootings last week, according to an analysis of the file by CNN.

• This weekend there were at least 12 mass shootings in the US.

President Joe Biden reacted to the San Jose shooting by urging Congress to "take immediate action" on gun legislation.

"Enough," Biden said Wednesday.

"Once again, I urge Congress to take immediate action and heed the call of the American people, including the vast majority of gun owners, to help end this epidemic of gun violence in America."

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The San Jose killings are also the latest against essential workers sustaining the United States economy during the COVID-19 pandemic, following high-profile shootings such as those in Indianapolis and Boulder, Colorado.

The VTA is a public transportation service that operates bus and light rail services in the Santa Clara Valley and employs about 2,000 workers.

The Santa Clara County Sheriff was unsure Thursday morning whether the attacker had specific targets in mind, she told CNN.

"I've heard those things, (but) I haven't heard them officially, so I'm not sure it was targeting certain individuals," Laurie Smith said.

Those killed, whose ages ranged from 29 to 63, were: Abdolvahab Alaghmandan, 63;

Adrian Balleza, 29 years old;

Alex Ward Fritch, 49;

José Dejesus Hernández III, 35 years old;

Lars Kepler Lane, 63;

Paul Delacruz Megia, 42 years old;

Timothy Michael Romo, 49;

Michael Joseph Rudometkin, 40;

and Taptejdeep Singh, 36, according to the Santa Clara County Coroner's Office.

They will be honored on Thursday night in an act in the Plaza del Ayuntamiento de San José.

Emergency personnel go to the scene of the shooting.

The shooter's home in San Jose was on fire at the time of the shooting, according to the sheriff.

The attacker has been identified as Sam Cassidy, a police source with knowledge of the investigation has confirmed to CNN.

Emergency calls about the shooting began just after 6:30 a.m. (PT), as employees on the midnight shift overlapped with those on the day shift, said Santa Clara County Deputy Sheriff Russell Davis.

Shortly after the shooting started, firefighters were called to a fire at the suspect's home in San Jose, the sheriff Smith told CNN Thursday morning.

It is not immediately clear how that fire started.

The attacker shot people inside two buildings in the maneuvering yard, Smith told CNN.

The yard is where VTA vehicles are kept and dispatched.

The attacker had two semi-automatic pistols and 11 magazines with ammunition, Smith told CNN.

"They were pistols of the type that would be legal in California," Smith said, adding that he did not know how or when the assailant obtained the weapons.

Sheriff's deputies and other law enforcement officers arrived while the shooting was taking place, within two minutes of the calls, as the sheriff's office has a nearby station.

They engaged the gunman on the third floor of a building in less than six minutes, Smith told CNN.

"I know for a fact that when the suspect learned that law enforcement was there, he took his own life," Smith told reporters previously.

He added that he believes the quick response from law enforcement agencies saved many lives.

During a search of the scene Wednesday, bomb-sniffing dogs alerted investigators to the assailant's locker at work.

In the locker, investigators found "explosive precursor stuff ... ingredients for a device," Smith said Thursday.

Smith did not know why the items were there or what the gunman might have intended for them, he said.

Cassidy resented her job and spoke angrily at her co-workers, says ex-wife

Cassidy, the identified attacker, was resentful of his job, his ex-wife Cecilia Nelms told CNN affiliate Bay Area News Group.

Nelms was married to Cassidy for about 10 years until the couple filed for divorce in 2005. She has not been in contact with her ex-husband for about 13 years, according to the outlet.

She often spoke in anger at her co-workers and bosses and sometimes directed her anger at her, Nelms told the outlet.

When they were married, he "resented what he considered unfair job assignments" and "ranted about his job when he got home," he said.

Cassidy also had a strained relationship with an ex-girlfriend, court documents show, which revealed troubling claims she made in a 2009 deposition in response to a restraining order he filed against her.

The woman says she dated Cassidy for about a year in what she says turned into an on-off relationship after about six months.

He described Cassidy as someone with mood swings that were "exacerbated when (Cassidy) drank large amounts of alcohol," he said in the court document, and claimed that he had bipolar disorder.

According to the court document, she said he enjoyed playing mind games with her.

"Several times during the relationship he became intoxicated, enraged and forced me sexually," said the ex-girlfriend, whose name has not been released by CNN, and who has been contacted for comment.

Emergency services leave a home under investigation in connection with the shooting.

Surveillance video shows a man leaving the suspect's home

Surveillance video obtained by CNN shows a man leaving the home of the suspect in the shooting Wednesday morning with a duffel bag.

A neighbor, who did not want to be identified, said the video was captured around 5:40 a.m. and shows Cassidy leaving the house in a pickup truck.

The neighbor described Cassidy as a "quiet" and "strange" man.

CNN has contacted the sheriff's office to see if investigators have seen and are aware of this video.

The neighbor later realized that a fire broke out at Cassidy's home around 6:30 a.m.

• Here's what we know about the San Jose, California shooting that left at least 9 dead

The fire was reported at 6:37 a.m., three minutes after calls began about the shooting, Smith, the sheriff, told CNN on Thursday.

No one was found inside the home, San José Mayor Sam Liccardo told CNN affiliate KGO.

Firefighters responded at a home in the 1100 block of Angmar Court in San Jose, according to tweets from the San Jose Fire Department.

That's about 8 miles from the VTA facility.

It took firefighters about an hour to extinguish the severe blaze, which caused extensive damage and left the structure uninhabitable, the fire department said.

–Jon Passantino, Sarah Moon, Eric Levenson, Stella Chan, Cheri Mossburg, Paul P. Murphy, Josh Campbell, Steve Almasy, Joe Sutton, Dan Simon, and CNN's DJ Judd contributed to this report.

California Shootings in the United States