LANSING, Mich. -- A surprise decision by Michigan prosecutors to drop all pending charges in the Flint water crisis and restart a three-year investigation is a reminder of the legal complexities surrounding the disaster.

Seven of 15 people had taken plea deals with no jail time, and their records will eventually be scrubbed clean. Eight others saw their charges dismissed Thursday, including two who served in former Gov. Rick Snyder's Cabinet. Some key questions and answers about the probe:

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WHAT CHANGED?

The announcement was a bombshell, but perhaps not entirely unexpected given the prosecution's recent trajectory. An investigation into the lead contamination and several deaths from Legionnaires' disease was taken over in January by newly elected Democratic Attorney General Dana Nessel. She was critical of her predecessor, Republican Bill Schuette, who decided in 2016 to hire outside special counsel Todd Flood to run the probe.

She named Solicitor General Fadwa Hammoud and Wayne County Prosecutor Kym Worthy to lead the cases. They voiced concerns about the thoroughness of the prior team's investigation, particularly its pursuit of evidence. Investigators in recent weeks used warrants to obtain the state-owned devices of Snyder and 66 other current or former state employees.

Nessel is not handling the criminal cases because of her role defending the state in Flint-related lawsuits, but she said Friday it was "very necessary" to drop the charges for now.

"To do a thorough and comprehensive and complete investigation, you obviously need to review each and every one of those documents and to look at all the devices," she told The Associated Press.

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WILL CHARGES BE REVIVED?

Maybe. The charges were dismissed without prejudice, meaning prosecutors could refile them, bring a new mix of charges or abandon the allegations forever. Hammoud and Worthy said they have identified additional persons of interest and new information.

Experts questioned if the most serious charge of involuntary manslaughter — which four of the eight defendants were facing — will be revived.

Criminal defense lawyer Neil Rockind, who is not involved in the cases, said it was a "stretch" to try to show that high-level officials such as former Michigan Health Director Nick Lyon through "gross negligence" directly caused two Legionnaires deaths by not warning the public of an outbreak in a timely fashion.

"That's a very tough allegation to prove," he said. "This just wasn't a case that was simple for the state to lay out, because the theories were so complex." Lyon's attorneys contend he had no "legal duty" to inform the public and that the medical community was told of the outbreak earlier.

They say there was no proof that the men in their 80s died from Legionnaires' disease, a type of pneumonia caused by bacteria that thrive in warm water and infect the lungs.

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WHY START OVER?

Peter Henning, a professor at Wayne State University Law School, said prosecutors want a "do-over" because they do not trust the prior probe and are worried there is evidence of which they may not be aware, including potentially exculpatory evidence that must be given to the defense.

He also questioned if the manslaughter charges will be refiled.

"I think they just want to go slowly on this and make sure that they have the right set of charges," he said. "We don't know if they're going to charge everyone again."

The announcement came a day before a Flint judge was due to affirm or throw out another judge's decision to send Lyon to trial. Lyon's team was optimistic it would have prevailed. But Nessel said of the defendants: "I wouldn't rest easy if I were them if there's real criminal culpability there."

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HOW LONG WILL IT GO?

Nessel said the investigation "can't drag on forever and ever" because of legal time limits to bring charges. She noted that Flint's water was switched in April 2014, and the statute of limitations for most crimes that may have been committed is six years.

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HOW MUCH HAS BEEN SPENT?

As of March 31, the state had spent $9.5 million on the prosecution. At least $9 million has been spent defending state employees who were charged, not including millions more that Snyder and his office spent related to criminal investigations and document requests.

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WHAT ARE THE POLITICAL DYNAMICS?

Flint residents are unhappy, because they feel no one has been held responsible for the contamination of their water supply during a period when the state managed the majority-black city of 100,000 and switched water sources to save money.

Water was pulled from a river without it being treated to reduce corrosive effects on old pipes, and a doctor reported high levels of lead in children.

Nessel said she questioned many of the cases because they were filed during the run-up to Schuette's gubernatorial campaign, and he "farmed them out to a private firm."

Schuette has defended his move as a way to prevent conflicts between him and his investigation team and the team defending the governor and state departments against water-related lawsuits. He said Thursday that the special counsel's office had 200-plus years of legal experience and conducted the probe "with the highest level of professionalism and expertise."

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