FLINT, Mich. (AP) — Michigan’s former director of disease control says she believes a spike in Legionnaires’ disease in the Flint area is related to a switch in the city’s water supply.

Corinne Miller says she shared her belief with her boss in January 2015, a year before the public was notified.

Miller is a key witness for prosecutors in their criminal case against Nick Lyon, head of the Michigan Health and Human Services Department. He’s charged with involuntary manslaughter in the death of a man who was diagnosed with Legionnaires’.

Miller testified Friday, the second day of a hearing that will determine if Lyon goes to trial as the highest-ranking official charged in the Flint water scandal. Miller pleaded no contest to willful neglect of duty and was put on probation.