The owner of the West Virginia coal mine where 29 men died in an explosion last year engaged in a cover-up, federal investigators say, to keep government inspectors in the dark about safety hazards.

The key act of deception that investigators attributed to the Upper Big Branch owner: Keeping two sets of books, and giving inspectors only a set that sanitized the records on safety threats.

As The Charleston Gazette reports, federal authorities found that managers with mine owner Massey Energy included problems such as spikes in methane levels and explosion-prevention equipment breakdowns in internal production reports — but left the information out of mine safety reports required by federal law.

Kevin Stricklin, coal administrator for the U.S. Mine Safety and Health Administration, said the actions by Massey’s Performance Coal Co. subsidiary could lead to felony criminal charges of falsifying safety records.

“They can keep five sets of books if they want,” Stricklin said during a briefing in West Virginia. “But they’re required to record the hazards in the official set of books.”

The MSHA maintains that Massey could have prevented the explosion, which caused the nation’s deadliest mine disaster in 40 years, by such safety steps as clearing out the mine’s coal dust buildup. The agency has rejected assertions by the former Massey chief executive, Don Blankenship, and the former chairman, Bobby Inman, that the April, 2010, blast was the result of a “natural disaster” involving an uncontrollable inundation of massive amounts of natural gas into the mine.

The federal investigators’ findings squared with, and expanded upon, a report issued by an independent team of state investigators this month. The federal report is expected to be completed this fall.

As The New York Times reports, a federal official said that two Massey employees, a foreman and a former chief of security, have been indicted in connection with the disaster. Both were accused of including lies in documents and other acts of deception. Eighteen executives refused to be interviewed for the federal investigation, invoking their Fifth Amendment rights.