GYOR, Hungary (Reuters) - A Hungarian court ordered a retrial on Monday over the spill of toxic red sludge in 2010 that killed 10 people in one of the country’s worst environmental disasters.

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Prosecutors had appealed against a 2016 ruling that acquitted 15 people in the case. Monday’s verdict by a court in the city of Gyor overturned that ruling and ordered a retrial.

In the 2010 spill, toxic red mud flowing from an alumina reservoir destroyed hundreds of homes in three towns and seeped into rivers including a tributary of the Danube.

It spread 1.9 million cubic metres of soft sludge, the colour of tennis clay, which emitted a pungent acidic smell that could be detected miles away. It took years to clean up.

“The court ... annuls the Veszprem court ruling dated January 28, 2016,” judge Csilla Zolyomi told a packed courtroom in Gyor.

She said there had been procedural mistakes and shortcomings in the hearing of witnesses at the Veszprem court with regard to the evaluation of expert opinions and also in the court’s justification for its acquittal ruling.

That prompted the Gyor court to order a retrial, which could be carried out by the Veszprem court, she said. “The new procedure will have to be conducted in an expedited manner ... and the evidence procedure has to be repeated,” the judge said.

MAL Corp, the aluminium smelting company that owned the faulty alumina reservoir, was subsequently taken over by the government, which declared it responsible for the incident and began to close it down.

In a first instance ruling, a court in the western town of Veszprem said that executives and top employees of MAL had not been criminally negligent, nor had they committed other crimes they were charged with during the 40-month legal procedure.

The prosecutors had asked for that ruling to be annulled, saying the Veszprem court ruling had drawn false conclusions in the case.