HALF MOON BAY, Calif. (AP) — A farmworker accused of killing seven people in back-to-back shootings at two Northern California mushroom farms was charged Wednesday with seven counts of murder and one of attempted murder.

Chunli Zhao, 66, was set to make his first court appearance Wednesday but it was postponed until Feb. 16, San Mateo County District Attorney Steve Wagstaffe said. His two attorneys did not immediately respond to calls and emails seeking comment.

Wagstaffe, speaking outside the courthouse, declined to share any additional details on a motive in the killing of Zhao's current and former coworkers, saying he wanted to keep the details out of the public eye to ensure a fair trial. Sheriff's officials have said it was workplace violence.

It was California’s third mass shooting in eight days, and the largest in San Mateo County's history, Wagstaffe said. It followed the killing of 11 people in the Los Angeles area amid Lunar New Year celebrations Saturday.

Authorities believe Zhao acted alone Monday when he entered a mushroom farm where he worked in Half Moon Bay, shot and killed four people and seriously wounded a fifth. He then drove to a nearby farm where he worked previously and killed three more people, said Eamonn Allen, a sheriff’s spokesperson.

Erlin Ortiz and her sister, Miriam Ortiz, pack mushrooms at the farm where Zhao is accused of killing four people.

They were sitting in their car after their shift when they saw Zhao, who was about 40 feet (12 meters) away, pull a gun from a backpack, shout something in Mandarin to a fellow Chinese farmworker and then shoot the man, they told the Bay Area News Group.

Zhao then shot a second worker, and gunned down the first worker who had gotten to his feet and tried to run away, Erlin Ortiz said.

“He was super red and very angry," she said of Zhao.

Shocked and horrified, Miriam Ortiz’s husband, who was behind the wheel, started the car and prepared to drive away.

Zhao turned to look at them, then hopped onto a forklift and headed toward an encampment on the farm where he and the sisters lived. His demeanor had changed, they said.

“He was laughing, he was smiling,” Erlin Ortiz said. “We saw him get on the forklift, and when he turned to see us, he was making fun of the situation.”

Erlin Ortiz said Zhao, who grew onions for himself and his wife in a little garden plot, would wave and greet them but always seemed serious.

The charges against Zhao include additional allegations that could result in the death penalty or life in prison without parole, though Gov. Gavin Newsom has issued a moratorium on executions. Among those allegations are that Zhao used a gun, caused great bodily injury and killed multiple people.

The coroner's office named six of the victims: Zhishen Liu, 73, of San Francisco; Marciano Martinez Jimenez, 50, of Moss Beach, California; Aixiang Zhang, 74, of San Francisco; Qizhong Cheng, 66, of Half Moon Bay; Jingzhi Lu, 64, of Half Moon Bay; and Yetao Bing, 43, whose hometown was unknown. The charging documents identify Jose Romero Perez as the other person killed and Pedro Romero Perez as the eighth victim, who survived the shooting.

Officials have said some of the people killed were migrant workers. Some people were shot in trailers on the property, Wagstaffe said.

Servando Martinez Jimenez said his brother Marciano Martinez Jimenez, one of the victims, was a delivery person and manager at one of the farms. He never mentioned Zhao or said anything about problems with other workers.

“He was a good person. He was polite and friendly with everyone. He never had any problems with anyone. I don’t understand why all this happened,” Martinez Jimenez said in Spanish.

Marciano Martinez Jimenez had lived in the United States for 28 years after arriving from the Mexican state of Oaxaca. Servando Martinez Jimenez said he is working with the Mexican consulate to get his brother’s body home.

It would not have been Zhao’s first fit of workplace rage, the San Francisco Chronicle reported. In 2013, Zhao was accused of threatening to split a coworker’s head open with a knife and separately tried to suffocate the man with a pillow, the Chronicle reported, based on court documents.

The two were roommates and worked at a restaurant, and the man, identified as Jingjiu Wang, filed a temporary restraining order against Zhao that was granted but is no longer in effect. Wang could not be immediately reached, the Chronicle reported.

Zhao is from China and has lived in the United States for at least a dozen years, Wagstaffe said. He had legal paperwork to live in the country at one time and investigators were determining whether it was still valid, Wagstaffe said. They were also looking into his prior contact with law enforcement.

The shootings broke out at California Terra Garden, previously known as Mountain Mushroom Farm, and nearby Concord Farms.

The majority of farmworkers in the area are Latinos but the Mountain Mushroom Farm was one of the few that employed Asian workers, said Belinda Hernandez, executive director of ALAS, a farmworker advocacy group based in Half Moon Bay. She said that mushroom farms offer the benefit of year-round work.

David Oates, a California Terra Garden spokesperson, said that he did not know how long Zhao worked there and that he was one of 35 employees who had stayed when ownership changed. He declined to comment further Wednesday, saying he would defer to law enforcement. And Aaron Tung, part owner of Concord Farms, did not respond Wednesday to a request for additional comment.

Half Moon Bay is a small, laid-back, coastal and agricultural city about 30 miles (50 kilometers) south of San Francisco. Its sweeping views of the Pacific Ocean make it a popular spot for hikers and tourists, who flock there to surf and for an annual giant pumpkin festival.

The new year has brought six mass killings in the U.S. in fewer than three weeks, accounting for 39 deaths. Three have struck California since Jan. 16, according to a database compiled by The Associated Press, USA Today and Northeastern University. The database tracks every mass killing — defined as four dead, not including the offender — in the U.S. since 2006.

The shootings in Half Moon Bay and Monterey Park followed the killing of a teenage mother, her baby and four others at a home in California’s Central Valley on Jan. 16. Officials discussing the investigation mentioned a possible gang link to the killings. ___

This story has been corrected to say six people, not eight people, were killed in California’s Central Valley on Jan. 16.