Federal prosecutors said Friday they are investigating whether there was "willful criminal activity" by the company that operates the West Virginia mine where 29 workers died in an accident last month.
The U.S. attorney's office for the Southern District of West Virginia said in a letter that investigators are looking into actions by the mine's operator, Performance Coal, and its directors, officers and agents.
The letter, obtained by The Associated Press, asks the Labor Department to hold off pursuing dozens of civil cases against Performance for alleged mine safety violations.
Performance is a subsidiary of Massey Energy Co., which owns the Upper Big Branch mine.
Last month, federal law enforcement officials said the FBI had interviewed nearly two dozen current and former employees of Massey in the probe. But the Justice Department declined to publicly confirm there was a criminal investigation.
In the letter Friday, Assistant U.S. Attorney R. Booth Goodwin II saids his office wants to make sure the pending civil cases don't interfere with the criminal probe. He asks the Labor Department to delay 44 civil penalty cases against Performance for alleged mine safety violations at Upper Big Branch.
Goodwin said a number of the safety citations could form the basis of criminal penalties under federal mine laws.
A Massey spokesman has said previously that the company was not aware of the nature of the federal probe but that "we intend to cooperate in all phases of the accident investigation."
The company was repeatedly cited for problems with its methane ventilation system and other issues in the months before the accident. It was not immediately clear which safety citations federal prosecutors were examining as part of the criminal investigation.
Joe Main, director of the Mine Safety and Health Administration, said at a Senate hearing last month that Massey has a "troubling record" of safety violations and appeared to take a "catch-me-if-you-can" attitude toward workplace safety at the mine.
© Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.