A leading virologist reported on Thursday that the first known coronavirus patient was likely a vendor in a Wuhan market hawking domestic and wild animals. Michael Worobey’s analysis of the geographic pattern of China’s early COVID cases led him to suggest the virus came from an infected animal at the Huanan Seafood Market. The animal then passed the disease to a female vendor, who became symptomatic on Dec. 11, 2019.

The peer-reviewed article, published by Worobey in the academic journal Science, does not purport to definitively solve the mystery of the virus’ origins, but rejects previous findings by World Health Organization researchers that “patient zero” was an accountant with no links to any markets, labs, or mass gatherings.

Worobey, who is a specialist in the origins of viral epidemics, was one of 18 scientists who penned a letter to Science in May calling for all possible sources of the virus to be investigated—including the controversial “lab-leak” theory. But in his Thursday report, the virologist noted that more than half of the earliest known cases were among those with direct connections to the market. “It becomes very difficult to explain that pattern if the outbreak didn’t start at the market,” Worobey said.