(KRON) — Cal/OSHA cited two employers in Half Moon Bay this week following an investigation into workplace violence that killed seven agricultural workers on January 23. The shocking mass shooting was allegedly carried out by Chunli Zhao, an angry 66-year-old farmworker who had worked for California Terra Garden and Concord Farms.

San Mateo County prosecutors said Zhao was “angry at several co-workers over perceived mistreatment.”

Zhao lived in a tiny shack at California Terra Gardens. County supervisors said the tragedy and following investigations exposed “deplorable” living conditions on the farms, wages as low as $9 a day, and several incidents of past violence.

Zhao lived with his wife in this shack at California Terra Gardens. (Image courtesy Supervisor Ray Mueller)

On Monday Cal/OSHA state labor authorities cited California Terra Garden, Inc. for 22 violations, including five classified as “serious,” for failing to have a plan or procedures to immediately notify employees of an active shooter threat and instruct them to seek shelter. Total proposed penalties are $113,800.

California Terra Garden and Concord Farms were both cited for failing to establish a workplace safety plan that evaluated the threat of workplace violence and train workers in a language they can understand, according to OSHA. Many of the farmworkers were immigrants who spoke Spanish or Mandarin.

Both employers were also cited by OSHA for failure to secure labor camp permits for onsite worker housing.

Concord Farms was cited for 19 total violations for failing to address previous incidents of workplace violence, and failing to develop procedures to correct and prevent this hazard, according to OSHA. Total proposed penalties are $51,770.

The Half Moon Bay mass shooting suspect is taken into custody on Jan. 23, 2023. (KRON4 Image)

California Terra Garden also had violence breakout prior to the mass shooting, according to court documents.

Yetao Bing, one of the seven farmworkers shot to death in January, survived a separate shooting last summer. Bing, 43, lived in a trailer at California Terra Garden. Last summer, another farmworker fired a gun through two trailers, including the trailer that Bing lived in, court documents state.

Investigators said Zhao killed four coworkers, and wounded a fifth, at California Terra Garden. He then allegedly drove to nearby Concord Farms where he fatally shot three more workers.

Chunli Zhao wipes a tear during a hearing at the San Mateo County Hall of Justice in Redwood City on Feb. 10, 2023. (Dai Sugano/Bay Area News Group/Pool)

Zhao is charged with seven counts of murder and one count of attempted murder. If convicted, he could face the death penalty. Longtime District Attorney Steve Wagstaffe said the killing spree was the worst mass shooting in San Mateo County’s history.

Other state agencies are continuing to investigate the farms and employers, which may result in additional enforcement actions, OSHA officials said.