The head of the Michigan health department, Nick Lyon, was charged Wednesday with involuntary manslaughter and misconduct regarding Flint’s lead-contaminated water.

This is the highest-ranking member of Gov. Rick Snyder’s administration to be charged in a criminal investigation.

Chief Medial Executive Eden Wells was also charged with obstruction of justice and lying to a police officer. Both are charged in connection with the Legionnaires’ disease outbreak in the Flint area that led to 12 deaths after the city’s water supply was switched to the Flint River in April 2014.

The crisis began when blood samples from young children from Flint, Michigan showed that they had much more lead in their blood due to lead seeping into the city’s pipes when they began using local drinking water in an effort to cut costs.

“This crisis was entirely preventable, and a startling reminder of the critical need to eliminate all sources of lead from our children’s environment,” Patrick Breysse, director of CDC’s National Center for Environmental Health, said in a news release.

According to the accusations, Lyon was aware about the outbreak of Legionnaires’ disease, but “took no action to alert the public of a deadly” outbreak until about a year later, Seipenko said. His failure to act resulted in the death of at least one person, special agent Jeff Seipenko told a judge. If Lyon is convinced, he could be facing up to 15 years in prison.

The investigation is attempting to determine “what, if any, Michigan laws were violated in the process that resulted in the contamination crisis currently forcing Flint residents to rely on bottled water for drinking, cooking and bathing as they fear for their health.”

Michigan Attorney General Bill Schuette has so far charged over a dozen current or former government officials linked to the Flint water crisis.