A California transit employee killed eight co-workers and wounded another before taking his own life on Wednesday,the latest in a spate of deadly U.S. mass shootings, prompting the state’s governor to ask: “What the hell is wrong with us?”

Authorities did not immediately offer many details or a possible motive for the shooting, which unfolded about 6:30 a.m. Pacific Time (1330 GMT) at a light-rail yard for commuter trains of the Santa Clara Valley Transportation Authority (VTA), in the heart of Silicon Valley in the San Francisco Bay Area.

A bomb squad was searching the yard and adjacent buildings after at least one explosive device was found, Santa Clara County Sheriff's Deputy Russell Davis said at a news conference.

Sheriff Laurie Smith told reporters that gunfire was still going on when her first deputies arrived on the scene, and that the assailant took his own life, apparently when he became aware that police were closing in on him.

Officers never exchanged gunfire with the suspect, Davis said. Still, Smith credited swift action by sheriff's deputies, who rushed to the scene from their own headquarters next door to the rail yard, preventing what might have been a much greater loss of life.

Governor Gavin Newsom, appearing with Smith and others in San Jose, voiced exasperation at the frequency and regularity of gun violence in America.

"There is a sameness to this and that numbness, I think, is something that we are all feeling," Newsom said. "It begs the damn question, What the hell is going on in the United States of America? What the hell is wrong with us and when are we going to come to grips with this?"

The gunman, the eight victims shot dead, and a survivor who was hospitalized in critical condition were all employees of the transit agency situated near the city's airport, officials said. The victims were found in two buildings on the site.

Authorities did not release the gunman's name or age. The San Jose Mercury News and other media outlets identified him as Samuel Cassidy, 57, a maintenance worker at the yard.

Cassidy had worked for the transit authority since at least 2012, when he was listed as an "electro-mechanic," and was promoted to "substation maintainer" in 2015, according to records posted by the nonprofit website Transportation California.

Last year, he earned a salary of $102,000, plus benefits and $20,000 in overtime, the records showed.

The suspect and another individual filed domestic violence restraining orders against one another in 2009, three years after Cassidy divorced his spouse, according to online court records.

'Essential workers'

"A horrible tragedy has happened today and our thoughts and love go out to the VTA family," Glenn Hendricks, chairman of the VTA board, told reporters.

The shooting took place in a section of the rail yard where workers perform maintenance on vehicles, and was not in the facility's operations and control center, he said. Rail service on the commuter line was suspended after the shooting.

San Jose, a city of about 1 million residents, lies at the heart of Silicon Valley, a global technology hub and home to some of America's biggest high-tech companies.

"These are, and were, essential workers," San Jose's mayor, Sam Liccardo, said of the victims.

He confirmed in television news interviews that authorities had also responded to a fire at the home of the suspect that erupted at about the same time as the shooting.

Multiple fire department, police and bomb squad vehicles were still parked outside the suspect's house, along a cul-de-sac in southeastern San Jose, hours after the shooting.

An explosives-detecting robot sat in the street near the home while two bomb squad technicians entered the ranch-style house. Arson investigators along with agents of the FBI and U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives were also present.

President Joe Biden was briefed on the shooting, and his staff continued to monitor the situation while keeping in close contact with local officials to offer any assistance needed, the White House said.

"What's clear, as the president has said, is that we are suffering from an epidemic of gun violence in this country, both from mass shootings and in the lives that are being taken in daily gun violence that doesn't make national headlines," White House spokeswoman Karine Jean-Pierre told reporters.

Mass gun violence, commonplace in a country with one of the highest rates of firearm ownership in the world, has escalated considerably following a year-long lull as the United States emerged from the worst of the COVID-19 pandemic this spring.

Wednesday's incident was the latest of at least nine deadly U.S. mass shootings that have made national headlines in the past three months, starting with a string of attacks at Atlanta-area day spas in mid-March that claimed eight lives, and a rampage days later that killed 10 at a Colorado supermarket.

Last month, a former employee of an Indianapolis FedEx center shot eight workers to death before taking his own life. Earlier this month a man fatally shot his girlfriend and five other people before taking his own life at a birthday party in Colorado.

The United States saw at least 200 mass shootings in the first 132 days of this year, according to a report by the Gun Violence Archive, a non-profit research group that defines such incidents as those in which four or more people, other than the assailant, are shot, regardless of the number killed.