HALF MOON BAY, Calif. • A farmworker accused of killing seven people in back-to-back shootings at two Northern California mushroom farms will be charged with seven counts of murder and one of attempted murder, a prosecutor said Wednesday.

The charges will be filed before Chunli Zhao, 66, makes his first court appearance Wednesday afternoon, said Steve Wagstaffe, the district attorney for San Mateo County.

It was not immediately clear whether Zhao had an attorney who could speak on his behalf.

Authorities believe Zhao acted alone Monday when he entered a mushroom farm where he worked in Half Moon Bay and opened fire, killing four people and seriously wounding a fifth, San Mateo County sheriff’s officials said. He then drove to another nearby farm where he had previously worked and killed an additional three people, said Eamonn Allen, a sheriff’s spokesperson.

The sheriff’s office said it believes the shootings were “workplace violence” but has not further detailed a motive. It was California’s third mass shooting in eight days, including the killing of 11 in Monterey Park in the Los Angeles area amid Lunar New Year celebrations Saturday.

Zhao also faces a special circumstance allegation of multiple murder, as well as sentencing enhancements on each count for the use of a firearm, Wagstaffe said.

If convicted of the special circumstance, Zhao could face life in prison without the possibility of parole or the death penalty. Gov. Gavin Newsom issued a moratorium on executions in 2019.

Officials have not yet released the names of the five men and two women who died, nor the one man who was injured. Some were Asian and others were Hispanic, and some were migrant workers.

Servando Martinez Jimenez said his brother Marciano Martinez Jimenez, who was a delivery person and manager at one of the farms, was among those killed. Servando Martinez Jimenez said his brother 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, 50, 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.