A judge has suspended homicide cases against 22 people in the Samarco mine disaster that killed 19 and devastated a river valley in southeastern Brazil in 2015.
The decision signed July 4 but only made public Monday cites worries over illegal evidence gathering raised by lawyers for Samarco ex-CEO Ricardo Vescovi and former operations chief Kleber Terra.
They claim that police and prosecutors based evidence on communications that were intercepted outside of the court-authorized dates for wiretaps.
The ruling by Judge Jaques de Queiroz Ferreira said the concerns "raise two serious questions that could affect the annulment of the procedure from the start."
In the ruling, seen by AFP, the judge cited the inadmissibility of "illegally obtained evidence" and ordered the criminal cases suspended until a decision is reached on the claims.
In November last year, de Queiroz Ferreira had given the green light to homicide and environmental criminal indictments against the 22 defendants and four mining companies.
They are accused of responsibility in the November 5, 2015 collapse of an iron ore tailings dam in the Minas Gerais region run by Samarco, which is jointly owned by Australian mining giant BHP and Brazilian giant Vale.
Twenty-one people, including senior executives, faced charges of "qualified homicide" and environmental crimes. An engineer was charged with having falsely certified the dam as stable prior to its collapse.
De Queiroz Ferreira was tasked with deciding whether to bring the defendants to a jury trial.
The Samarco dam burst was branded Brazil's worst environmental disaster, drawing comparisons with the 2010 Deepwater Horizon oil rig explosion which killed 11 workers and triggered a devastating spill in the Gulf of Mexico.
Prosecutors denounced the mining companies for reckless policies "to boost profits and dividends."
Samarco says that the accident was impossible to foresee, and that it is compensating victims' families and helping to restore environmental damage.
The mining companies have agreed to pay billions of dollars in compensation.
In May 2016, prosecutors filed a civil lawsuit against Vale, BHP and Samarco seeking 155 billion reais ($49 billion). In July this year, Vale said that lawsuit had been suspended.