The FBI has interviewed almost two dozen current and former employees of Massey Energy Co., which owns the West Virginia mine explosion that killed 29 in early April, to determine whether there was criminal negligence in the disaster, a federal law enforcement official told CNN.
Federal probes are not unusual in mining disasters with many fatalities, said the official, who requested anonymity because the investigation is ongoing.
The Upper Big Branch mine, the site of the April 5 explosion, had been cited for hundreds of safety violations in 2009 and during the first three months of 2010.
The Mine Safety and Health Administration announced Tuesday that it had conducted inspections at three other Massey-owned mines in West Virginia since late March due to anonymous complaints of hazardous conditions.
An MSHA statement said it ordered that miners be withdrawn from particular areas of the three mines and issues "multiple citations for serious violations."
Also on Tuesday, a top federal mine safety official said that existing mining laws and regulations had not been properly enforced before the West Virginia disaster but pledged his agency will now use all its powers to do so.
Joe Main, the assistant secretary of labor for Mine Safety and Health, told a Senate committee that the MSHA will start using its power to immediately shut down mines engaging in unsafe behavior. Main said the authority has existed for decades but has never been used.