FLINT, Mich. (AP) — Michigan’s former health director was charged Thursday with involuntary manslaughter in the deaths of nine people who got Legionnaires’ disease during the Flint water crisis as prosecutors revisit how the city’s water system was contaminated with lead and bacteria during one of worst human-made environmental disasters in U.S. history.

Nick Lyon pleaded not guilty during an appearance in a Genesee County court. Moments later, his old boss, former Gov. Rick Snyder, also pleaded not guilty to misdemeanor charges of willful neglect of duty in Flint.

They were among several people summoned to court to face charges, the result of a renewed 19-month investigation launched by the attorney general's office after Dana Nessel, a Democrat, was elected.

The charges against Snyder carry up to a year in jail and a $1,000 fine upon conviction. No governor or former governor in Michigan’s 184-year history had been charged with crimes related to their time in that office, according to the state archivist.

Wearing a mask, Snyder, 62, said little during the brief hearing, which was conducted by video. He replied, “Yes, your honor,” when asked if he was living in Michigan.

“We believe there is no evidence to support any criminal charges against Gov. Snyder,” defense attorney Brian Lennon told reporters Wednesday night.

Snyder, a Republican, was governor from 2011 through 2018. The former computer executive pitched himself as a problem-solving “nerd” who eschewed partisan politics and favored online dashboards to show performance in government. Flint turned out to be the worst chapter of his two terms due to a series of catastrophic decisions that will affect residents for years.

The date of Snyder's alleged crimes in Flint is listed as April 25, 2014, when a Snyder-appointed emergency manager, Darnell Earley, who was running the struggling, majority Black city carried out a money-saving decision to use the Flint River for water while a pipeline from Lake Huron was under construction.

The corrosive water, however, was not treated properly and released lead from old plumbing into homes.

Despite desperate pleas from residents holding jugs of discolored, skunky water, the Snyder administration took no significant action until a doctor reported elevated lead levels in children about 18 months later.

“I’m sorry and I will fix it,” Snyder promised during his 2016 State of the State speech.

Prosecutors also charged Earley with two felony counts of misconduct in office Thursday. He pleaded not guilty.

Authorities counted at least 90 cases of Legionnaires’ disease in Genesee County during the water switch, including 12 deaths. Some experts found there was not enough chlorine in Flint's water-treatment system to control legionella bacteria, which can trigger a severe form of pneumonia when spread through misting and cooling systems.

It's the second time that Lyon has been charged with manslaughter, but the earlier case involved only two deaths. He was accused in 2017 of failing to timely warn the public about the outbreak, but that case was dropped by prosecutors when they decided to take a fresh look at evidence.

An involuntary manslaughter conviction carries up to 15 years in prison and a $7,500 fine.

Lead can damage the brain and nervous system and cause learning and behavior problems. Flint's woes were highlighted as an example of environmental injustice and racism.

The criminal investigation has lasted five years under two teams of prosecutors. Todd Flood, who got misdemeanor convictions from seven people, was ousted in 2019 after the election of Nessel. Fadwa Hammoud subsequently dropped charges in eight pending cases and said the investigation would start over. She said the first team had failed to collect all available evidence.

Separately, the state, Flint, a hospital and an engineering firm have agreed to a $641 million settlement with residents over the water crisis, with $600 million coming from Michigan. A judge said she hopes to decide by Jan. 21 whether to grant preliminary approval. Other lawsuits, including one against the U.S. Environmental Protection Agency, are pending.

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White reported from Detroit and Eggert reported from Lansing, Mich.