Edwards is the independent Virginia Tech researcher who found lead in Flint's drinking water back in 2015, when state officials still denied it was leeching into the water supply.
The engineering professor says he recreated the crisis in his lab this winter and found that the corrosive water created an environment where bacteria could flourish.
"What we discovered was that when the Flint River water went into the system it released a lot of iron, and removed the disinfectant from the water," Edwards said. "And in combination, those two factors, the iron as a nutrient and the disinfectant disappearing, allowed legionella to thrive in buildings where it could not do so previously."
Flint's water crisis happened because state officials made a temporary switch in the water supply and did not properly treat the water with an anti-corrosive agent. That decision caused the harsh water to eat away at the pipes as it traveled to homes. Lead pipes leeched lead into the water, poisoning hundreds. Iron pipes leeched iron, Edwards said - and created the conditions for the Legionnaires outbreak.
"The triggering event was very clearly the use of Flint River water without any corrosion control," Edwards said.
"Had the corrosion control been in the water, disinfectant would have been higher, iron would have been lower, probably the outbreak would not have occurred."
Investigations into the outbreak
Edwards' experiment compared bacteria levels of corrosive Flint water in his lab to levels in properly treated water in Detroit. He has been studying what happened in Flint since before the crisis was even acknowledged by the state of Michigan. Edwards predicted during the water crisis that a lack of corrosion control could lead to a Legionnaires outbreak.
"It was only later that we realized that one was, it just wasn't public knowledge," Edwards told CNN.
Legionnaires' disease is a respiratory bacterial infection usually spread through mist that comes from a water source; it isn't spread person-to-person. Symptoms include fever, chills and a cough.
The Flint outbreak was one of the largest in U.S. history, and Edwards said it's likely the first to originate in a drinking water system. Twelve people died, and almost 90 were sickened during two waves of the outbreak in 2015.
There has never before been a scientific link to the cause of the Flint outbreak, because, as a CNN investigation revealed last spring, state officials allegedly stopped the U.S. Centers for Disease Control and Prevention from coming to Flint to determine the cause during the first wave of the outbreak.
Even though the CDC said it wanted to investigate, the CDC said the state insisted on handling it. Michigan did provide assistance, but never found the cause of the outbreak.
According to CDC protocol, a state must "invite" the CDC to investigate an outbreak, and the county said Michigan did not do that.
Michigan officials said they believed they had the expertise to do a proper investigation, saying "we were able to meet the epidemiological case investigation need in the county. CDC was a part of these conversations as they were involved in many aspects of the investigations."
Edwards said of the CDC, "not having the world's foremost experts on legionella come to Flint and diagnose the cause of this outbreak was really unfortunate, not just from the perspective of samples not being collected, but probably the CDC could have forced action earlier that could have prevented further outbreaks and deaths that actually occurred in 2015."
'Every piece of this is important'
So, as prosecutors move forward with a criminal investigation into the deaths in Flint, they don't have hard proof that the water crisis caused the outbreak of Legionnaires.
"Every piece of this is important," said Bill Schuette, Michigan's attorney general, who has been leading the criminal investigation into what happened in Flint. Already he's charged people in connection with the outbreak. Emails obtained show that in late 2014, state officials were questioning whether the epidemic was related to the water source.
But the state has maintained that Flint's McLaren hospital was the culprit, since many of the patients contracted the disease after being treated there.
In February, the CDC found a genetic link
-- a matching strain of legionella -- between the city's water system and three patients who were diagnosed. It found that at least one patient who fell ill was never in contact with the hospital.
But that just led to more questions. The state is saying the hospital caused the outbreak, and the hospital is saying the state caused it.
"And the reality is, they both did," Edwards said, adding that the ultimate responsibility for preventing the spread of disease at the hospital falls to the hospital.
In a statement, to CNN, the Michigan Department of Health and Human Services said it will "carefully consider" Edwards' findings.
"We have great respect for Dr. Edwards and his work. But we are not aware of water samples from the city of Flint water system that genetically link to any cases, as would be necessary to make a causal determination."
The hospital said it also welcomes the research.
"We have not seen the same level of concern or scientific diligence from officials with the Michigan Department of Health and Human Services, so we welcome the researchers' ongoing efforts and hope they are able to increase the volume on this important discussion," McLaren Hospital said in a statement.
The state's "continued attacks" on McLaren and the "lack of action" from the state has been "staggering," the statement said.
Edwards said he has legionella samples from Flint's water during the outbreak and he is trying to match them to the samples from patients. But 100% scientific certainty may never be known.
"It's difficult to do that -- because you're trying to go back in time. whether anyone does that or not, remains to be seen," Edwards said. "What our experiment is going to do is show why the Flint river water was growing more legionella. This is the only way you can do that testing becuase that water doesn't exist anymore, we had to recreate it," he said.
Schuette told CNN that part of his investigation will look at the potential that there were more deaths caused by Legionnaires that were misdiagnosed or improperly diagnosed as hospital officials tried to contain the crisis.
"Whether it's 12 or 15 or whatever the number is, people died from the water in Flint, and accountability has to be delivered," Schuette said.
Already, the Michigan Attorney General's office has brought charges against 13 people, including some accused of covering up the outbreak.
"There are some people who altered figures. There are some people who monkeyed with the figures," Schuette said. "I think there was too much of an attitude of balance sheets and figures instead of safety and making sure the water system worked right. And that attitude I think was corrosive, as well, and I think far too prevalent."
In his office, Schuette said he keeps a reminder of the victims -- a nametag of the daughter of a man who died.
She approached Schuette at an event and thanked him.
"Feeling that, being around that, really underscored the significance of what this investigation was about," he said.