The security chief of Massey Energy's Upper Big Branch mine was arrested Monday and charged with obstructing the investigation into last year's explosion that killed 29 miners, the first criminal charges stemming from the worst U.S. mining disaster in 40 years.

Hughie Elbert Stover, who also headed security at two other Massey operations, was indicted last week by a federal grand jury in West Virginia on charges of lying to the FBI and trying to dispose of key documents. The indictment was unsealed Monday.

Stover provided personal security for former Massey chief executive Don L. Blankenship, who retired in December, according to sources familiar with the federal and state investigations into the mine accident. "He was very very close to Blankenship,'' said one source, who spoke on condition of anonymity because the probe is continuing. "He would drive Blankenship places. He called him 'Mr. B.'â''

The indictment offers no insight into the cause of the April 5 blast at the Montcoal, W.Va., mine, which is owned by Richmond-based Massey. But experts said the charges suggest that the Justice Department is exploring possible criminal liability. Massey had been cited for numerous safety violations before the explosion.

"They are being thorough and they are being comprehensive,'' said Davitt McAteer, chair of an independent West Virginia state commission that also is probing the disaster. McAteer is a former head of the federal Mine Safety and Health Administration.

It is unclear whether an attorney for Stover has been named. Stover has not entered a plea; he is scheduled to appear in federal court March 15.

Shane Harvey, general counsel for Massey Energy, said the company notified the Justice Department "within hours" of learning that documents sought by investigators had been disposed of and took steps to recover the papers and turn them over to the government.

"The Company takes this matter very seriously and is committed to cooperating with the U.S. Attorney's office,'' Harvey said in a statement.

Sources familiar with the Justice Department's criminal investigation described it as expansive. They said it was focused on the explosion, whether safety procedures designed to prevent the blast were followed and whether any documents were destroyed to cover up the cause.

Investigators reportedly have run into several obstacles. About 270 people have been interviewed, but about 15 others - including Blankenship, Massey's head of safety and the foreman of the Upper Big Branch mine - have declined to speak to investigators, sources said.

Even if the FBI finds evidence of criminal wrongdoing beyond obstructing justice, it might be difficult to bring a substantial case, mine safety experts said.

"If you had a superintendent instructing someone, 'We don't have time to fix that unsafe condition or clean up all this coal dust, let it go until next week,'' that's not a felony'' under the Federal Mine Safety and Health Act, said Tony Oppegard, a lawyer and former top Mine Safety and Health Administration official.

Sources familiar with the investigation said prosecutors will likely seek Stover's cooperation in the inquiry and question him about his ties to Blankenship.

A Massey spokesman declined to comment beyond the company's statement.

Stover, 60, was arrested on Monday at his home in Clear Fork, W.Va., on charges of obstruction of justice and making false statements. He works for Performance Coal Co., a Massey subsidiary that operates the Upper Big Branch mine.

The indictment charges that Stover lied to an FBI agent and an investigator for the mine safety administration who were probing allegations that security guards at Upper Big Branch routinely notified mine workers when federal inspectors had arrived at the facility. Such notification could prevent inspectors from fully evaluating the mine's operations.

Stover, the indictment said, denied that such a practice existed and told agents that he would have fired any security guard who provided such advance notice. In reality, the indictment says, Stover personally instructed security guards to notify mine personnel whenever federal inspectors arrived at the mine.

The indictment also charges Stover with attempting to impede the federal investigation by directing someone, whose identity was not revealed, to dispose of thousands of pages of documents stored in a Massey building near the mine. The documents, which had been discarded, included information about earlier federal inspections, according to the indictment.