Virginia Tech Professor Marc Edwards released to CNN the unpublished results of a study that show the Flint water crisis most likely caused the deadly outbreak of Legionnaires disease that killed at least 12 people since 2014.

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.

“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.