WASHINGTON - The Justice Department has launched a criminal investigation of the April 5 explosion at Massey Energy's Big Branch mine in West Virginia, law enforcement sources said.

The case originated in the U.S. attorney's office in the Southern District of West Virginia, which has prosecuted the coal company for criminal violations of safety standards in the past. A spokesman for that office referred questions to the Justice Department press office in Washington, which declined all comment.

Massey spokesman Jeff Gillenwater said the company is aware that investigators are interviewing witnesses at the Big Branch mine but is "not aware of the nature of their investigation. We intend to cooperate in all phases of the accident investigation."

The FBI has interviewed nearly two dozen current and former employees, a federal law enforcement official said Friday. The mine explosion killed 29 men.

The official said that in the interviews over recent days the FBI has been looking for any evidence that the company engaged in criminal negligence. The official spoke on condition of anonymity because the inquiry has not been made public. The FBI declined to comment on the matter at its headquarters in Washington.

Massey paid one of the biggest fines in the history of mining following the Aracoma Mine fire in 2006. In that case, Massey pleaded guilty to criminal charges and also paid civil fines related to federal Mine Safety and Health regulatory violations.

In 2007, the operator of Massey's White Buck mine in West Virginia was fined $50,000 for a criminal mine safety violation and a shift foreman was given a year of probation after pleading guilty to a misdemeanor charge of not performing safety examinations. As part of a plea agreement, prosecutors dropped a felony complaint that the company had falsified records to indicate that pre-shift safety reviews had been conducted.

Mine safety officials have suggested that a preventable buildup of explosive methane gas and coal dust was the likely cause of the April 5 disaster. The mine had been cited for hundreds of safety violations in the 18 months before the accident.

Also Friday, President Barack Obama issued a statement saying his administration is taking steps to demand accountability for safety violations and to "strengthen mine safety so that all of our miners are protected."

The Labor Department also is investigating the explosion, prompted in part by strong statements from Obama, who attended a memorial service for the miners and has called for renewed attention to worker safety.

At a congressional hearing this week, a Mine Safety and Health Administration official said that Massey appeared to take a "catch-me-if-you-can" attitude toward safety regulation and compliance. With AP

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