DETROIT — Prosecutors dropped all criminal charges Thursday against eight people in the Flint water crisis and pledged to start from scratch the investigation into one of the worst man-made environmental disasters in U.S. history.

The stunning decision comes more than three years — and millions of dollars — after authorities began examining the roots of a scandal that left Flint’s water system tainted with lead. Michigan Solicitor General Fadwa Hammoud, who took control of the investigation in January after the election of a new attorney general, said “all available evidence was not pursued” by a previous team of prosecutors.

“This week, we completed the transfer into our possession millions of documents and hundreds of new electronic devices, significantly expanding the scope of our investigation,” Hammoud and Wayne County prosecutor Kym Worthy said in a statement.

“Our team’s efforts have produced the most comprehensive body of evidence to date related to the Flint water crisis. We are now in the best possible position to find the answers the citizens of Flint deserve and hold all responsible parties accountable,” they said.

Hammoud’s team recently used search warrants to get state-owned mobile devices of former Gov. Rick Snyder and 66 other people from storage.

Among those who had charges dismissed: Michigan’s former health director, Nick Lyon, who was accused of involuntary manslaughter for allegedly failing to timely alert the public about an outbreak of Legionnaires’ disease when Flint was drawing improperly treated water from the Flint River in 2014-15.

Lyon’s attorney, Chip Chamberlain, said they “feel fantastic and vindicated.”

Although prosecutors cautioned that Lyon and others could be charged again, Chamberlain said he’s not worried.

“We’re confident that a just and fair investigation, done properly, will yield no evidence of any criminal wrongdoing,” Chamberlain said.

While waiting for a new pipeline to bring water from Lake Huron, the majority-black city of 100,000 pulled water from a river without treating it to reduce corrosive effects on old pipes. Lead infected the distribution system in a community where 41% of residents are classified by the government as living in poverty.

Due to poor finances, Flint was being run by financial managers appointed by Snyder. The uproar over water quality reached a peak by fall 2015 when a doctor reported high levels of lead in children, which can cause brain damage.

Some experts also have linked the water to Legionnaires’ disease, a type of pneumonia caused by bacteria that thrive in warm water and infect the lungs. People can get sick if they inhale mist or vapor, typically from cooling systems.

Flint’s water no longer comes from the river and has significantly improved, but some residents are so distrustful that they continue to use bottled water.

The criminal probe began in 2016 when Bill Schuette was attorney general. He hired a Detroit-area lawyer, Todd Flood, as special prosecutor. Andy Arena, the former head of the FBI in Detroit, was a key investigator.

No one is behind bars. Seven of 15 people charged pleaded no contest to misdemeanors. Their records will eventually be scrubbed clean.

Charges were pending against eight people, including former Michigan chief medical executive Eden Wells and two men, Gerald Ambrose and Darnell Earley, who were state-appointed emergency managers in Flint. Like Lyon, Wells was charged with involuntary manslaughter.

“We understand that there will be further investigation, but do not expect it to justify any further prosecution relative to her,” Wells’ attorneys, Steven Tramontin and Jerold Lax, said.

Through February, Flood’s team had spent $8.2 million, records show. State government separately has spent millions of dollars to provide defense lawyers to public employees charged in the case.

Hammoud dismissed Flood in April and put together a new team. He didn’t immediately respond to a request for comment on the dismissal of charges Thursday.

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