A farmworker charged with killing seven people at two mushroom farms in California told police he carried out the shootings after his supervisor demanded he paid $100 (£81) to repair a damaged forklift truck.

San Mateo County District Attorney Steve Wagstaffe told the Bay Area News Group that Chunli Zhao was enraged by the equipment bill, saying that a co-worker was to blame for the collision between his forklift and their bulldozer.

Authorities say Zhao, 66, shot and killed four workers and wounded a fifth employee on 23 January at California Terra Garden in Half Moon Bay, a city around 30 miles south of San Francisco.

He is accused of then going to nearby Concord Farms, where he had worked previously, and shooting dead three former colleagues.

Zhao previously told NBC affiliate KNTV-TV in a courthouse interview that he committed the shootings.

He said he was bullied and worked long hours on the farms and his complaints were ignored, the station reported.

Zhao said he had reportedly vented to his supervisor about the bill, but that the supervisor insisted he needed to pay. Zhao then allegedly shot the supervisor and the co-worker, the news outlets reported.

Speaking in Mandarin, Zhao told the television station from a county jail in Redwood City that he had been in the US for 11 years and had a green card.

He said he had a 40-year-old daughter in China and lived with his wife in Half Moon Bay.

The coroner’s office has 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 identified Jose Romero Perez as the other person killed and Pedro Romero Perez as the eighth victim, who survived.