Brazilian federal police have proposed criminal charges against mining giant Vale and German safety firm Tüv Süd and 13 of their employees over January's deadly dam collapse, reports say.
Police reportedly say both firms used falsified documents that said the Feijão dam was stable.
At least 248 people were killed as a sea of mud engulfed a staff canteen, offices and nearby farms.
The collapse was Brazil's worst industrial accident.
Twenty-two people are still missing.
Seven people from Vale and six from Tüv Süd are being indicted, O Globo reported.
Vale says it has been made aware of the federal police report. Tüv Süd declined to comment.
In July a Brazilian judge ordered Vale to pay compensation for all damages caused by the collapse of the dam, saying that that the company was responsible for fixing all the damages including the economic effects.
The same month, emails emerged that showed Tüv Süd's own analysis of the dam initially failed to meet official requirements.
Read more on the dam collapse:
Tüv Süd inspected the dam in the months before the collapse. It was a "tailings" dam - an embankment filled with waste product - and decades of waste from the nearby mine had been piled up and grassed over.
Tailings dams are vulnerable to "liquefaction", when, for various reasons, the solid material begins to act and move like a liquid, putting them at risk of becoming vulnerable to collapse.
Documents and internal emails seized by investigators show that Tüv Süd employees knew for around a year that there was liquefaction at the dam.
Also in July, Brazil's Senate urged prosecutors to bring charges ranging from environmental damage to involuntary manslaughter against top managers at Vale at the time of the dam collapse.
At the time Vale insisted that senior company officials had not been aware of any "imminent risks" at the dam prior to its collapse.
There are also concerns that other dams may be at risk of collapse.