Russian investigators say deliberate tampering with an electronic gauge was partly to blame for explosions at a Siberian mine which killed 108 people.
Officials said it was modern Russia's worst mine disaster
The head of a technical supervision body, Konstantin Pulikovsky, said the tampering resulted in the gauge showing a lower reading of methane gas.
Sparks from an exposed cable were also blamed for the blasts at the Ulyanovskaya coal mine last month.
The Russian federal body Rostekhnadzor has been investigating the disaster.
Mr Pulikovsky said his team had established that several explosions happened at the mine - first methane gas exploded, then coal dust, Interfax news agency reported.
The accumulation of coal dust in the mine was higher than normal, he said.
"The readings on the mine's meters and on the remote server were deliberately lowered and neither the operators nor the monitors were able to know the real quantity of methane in the mine," said Mr Pulikovsky.
The Kemerovo regional governor, Aman Tuleyev, said "the intentional blocking" of the mine safety system was done "consciously in order to increase coal production". The mine is situated in the Kemerovo region.
Russian officials said the Ulyanovskaya disaster was the worst mining accident in Russia's modern history.
Virtually the whole of the mine's management died, and a British engineer was also among the dead.
Ninety-three people were rescued.
Rescuers described a scene of utter devastation, with collapsed and flooded mineshafts and bodies ripped apart.
Many of Russia's mines have poor safety standards and have not been updated since the fall of communism.
But the Ulyanovskaya mine was opened only four-and-a-half years ago and had been fitted with modern equipment, officials said.