A farmworker charged with killing seven people at two Half Moon Bay mushroom farms reportedly told investigators he was spurred to carry out the shootings after his supervisor demanded he pay $100 to repair a forklift damaged at work.

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

KNTV-TV, the NBC affiliate in the San Francisco Bay Area, was first to report the development.

Authorities say Zhao, 66, shot and killed four workers and wounded a fifth employee Monday at California Terra Garden. He then went to nearby Concord Farms, where he had worked previously, and fatally shot three former co-workers.

Zhao told KNTV-TV in a courthouse interview Thursday 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.

On Monday, Zhao vented to his supervisor about the bill, but 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 has been in the U.S. for 11 years and has a green card. He said he has 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.

— The Associated Press