A German safety inspection firm reportedly certified a dam in Brazil that collapsed in January, killing nearly 300 people, despite concerns that it wasn't safe, a new report claims.

Tüv Süd was hired by Vale, a Brazilian mining company to certify its tailings dam near its iron-ore mine in Brumadinho, and reportedly changed its certification process for the dam after acknowledging in internal emails that it was unlikely to pass inspection, according to the BBC. It has also stopped cooperating with the investigation.

Tailings dams are made of piled up waste and grass and are vulnerable to collapse if the solid material that makes up their structure starts to weaken in a process called liquefaction. Investigators looking into the collapse have found that Tüv Süd — knowing the dam in Brumadinho had a liquefaction problem — changed the standard by which it was certified by attaching conditions like a ban on explosives near the structure in order for it to pass, according to the BBC

"In a criminal process it's natural the accused don't want to explain everything," Brazilian Congresswoman Aurea Carolina told the BBC of the company's lack of cooperation. "But this is a disaster of great magnitude with a shockingly high number of victims. It's unprecedented in Brazil."

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The BBC reported investigators have seen documents from Tüv Süd acknowledging liquefaction at the dam about a year before it collapsed earlier this year, covering the nearby countryside with toxic brown sludge and killing hundreds of people who had no time to get out of the way. Investigators also know of a failed attempt to fix liquefaction at the dam in June 2018, about six months before the collapse

Internal Tüv Süd emails translated from Portuguese express worry about the safety of the dam throughout 2018.

"We're finishing the studies about liquefaction of the dam B1, but everything points that it won't pass," one email from May 2018 says.

"The results leave us in a very vulnerable position," says another two days later.

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A third email from November, just a couple months before it finally gave out, says, "This dam has a liquefaction problem."

Vale had fired two auditing firms that refused to certify the Brumadinho dam before hiring Tüv Süd.

Now, as Brazilian prosecutors and officials are looking into the disaster, Tüv Süd is, "as a corporation choosing to remain silent," state prosecutor William Garcia Pinto Coelho told the BBC.

"I have no doubt that a more collaborative approach might bring new light to the case and also clarify what happened behind closed doors," he said.

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Vale maintains it was not at fault for the collapse, saying internal and external audits showed the dam was structurally sound. Tüv Süd says it is cooperating with the investigation, despite contrary statements from Brazilian authorities. The German government told the BBC it has no responsibility to ensure Tüv Süd works with Brazilian investigators.

Earlier this month a Brazilian Senate committee recommended charges against Tüv Süd for its corporate responsibility for the tragedy and called for Vale's chief financial officer and former CEO be indicted for murder, according to Reuters.

Fox News' Tyler Olson contributed to this report.