Chunli Zhao, who is charged with killing seven people in a series of shootings at two Northern California mushroom farms, pleaded not guilty on Thursday.
Mr Zhao, 66, wore a red prison jumpsuit and said little during the hearing, answering questions through a Chinese translator, the San Jose Mercury News reports.
The Chinese national is accused of killing seven people in January at the farm where he worked, as well as another from which he had been fired in 2015.
In an interview with NBC Bay Area, Mr Zhao admitted to the shootings, saying he was remorseful. He said he resented his employers for what he described as years of unaddressed bullying and long hours.
He added that he purchased his gun legally, and thought he might suffer from an undiagnosed mental illness.
The alleged gunman was arrested following the shootings on 23 January. He was found sitting in his vehicle in the parking lot of a sheriff’s substation. A police search revealed a semiautomatic weapon in the car.
Officials say they’re still searching for a concrete motive.
“There was nothing that would have kind of elevated or raised us to have any concern with him at this time, prior to this incident,” San Mateo county sheriff Christina Corpus told CNN, describing how he wasn’t previously on the radar of law enforcement .
The shootings at the mushroom farm have raised questions about working conditions on the two farms in the coastal hamlet of Half Moon Bay.
San Mateo County Supervisor Ray Muller inspected the site of one of the shootings and found it “deplorable.”
"No one is going back to live there," he said at the time, adding, "Horrible. Horrific. Deplorable conditions. We saw what basically looked like sheds. Storage containers that people were living in. No insulation. No running water. Nowhere where you would want to prepare food."
(The company which owns the farm told ABC7 News employees living on-site had kitchens, bathrooms, showers, and other standard living amenities.)
Mr Zhao was the subject of a temporary restraining order in 2013, from a roommate who said the man violently threatened him and attempted to suffocate him while the two were living together in San Jose and working at a restaurant.
“While I couldn’t (breathe), I used all my might within the few seconds to push him away with my blanket,” the roommate wrote in court documents.
