Prosecutors investigating the deadly lead-poisoned water crisis in Flint, Michigan, dropped criminal charges against eight people, including the former head of the state's health department.

The Department of Attorney General said in a press release on Thursday that the decision to dismiss the charges is "not a determination of any defendant’s criminal responsibility" and stems from concerns over how the Office of Special Counsel handled the investigation.

According to officials, the OSC "entered into agreements that gave private law firms" a role in deciding what information would be turned over to law enforcement.

The eight criminal cases involved various crimes, including involuntary manslaughter, for failing to alert the public about an outbreak of Legionnaires' disease in 2014 and 2015 that killed at least 12 people.

The outbreak occurred at the same time Flint's water system was contaminated with lead.

Among those charged was Nick Lyon, who was then the director of the Michigan health department. Lyon was charged with involuntary manslaughter.

Special agent Jeff Seipenko told a judge that Lyon was made aware of the outbreak in January 2015 but did not alert the public until nearly a year later. Seipenko said Lyon's failure to tell the public resulted in at least one person dying.

Dr. Eden Wells, the state's chief medical officer, was also charged with involuntary manslaughter as well as lying to a special police agent and obstruction of justice, according to The Detroit News.

"We are not precluded from refiling charges against the defendants or adding new charges and additional defendants," said Solicitor General Fadwa Hammoud and Wayne County Prosecutor Kym L. Worthy in a joint statement.

Michigan Attorney General Dana Nessel said Thursday that she supports Hammoud and Worthy's decision to dismiss the charges if it helps them conduct a "comprehensive and complete investigation."

The city of Flint began using the Flint River as its water supply in 2014, but did not treat it for corrosion after lead from old plumbing seeped into the water. Some experts have said that the contaminated water led to an outbreak of Legionnaires' disease, a severe form of pneumonia caused by bacteria that thrives in warm water.

In 2014 and 2015, there were nearly 100 cases of the disease in the Flint area, resulting in the deaths and sickening another 72 people.