Massey Energy used a double-accounting system to deceive inspectors at a West Virginia coal mine where 29 men died, regulators said Wednesday. Kevin Stricklin of the U.S. Mine Safety and Health Administration said the company kept internal records of safety problems at the Upper Big Branch mine and of what had been done to correct them, The New York Times reported. But the records were not transferred to official books made available to state inspectors. \"If a coal mine wants to keep two sets of books, that\'s their own business,\" Mr. Stricklin said. \"What they have to do is record the hazards associated with the examination in the official record book, and that wasn\'t the case here.\" The explosion in April 2010 was the worst in U.S. mining in four decades. Stricklin, presenting the findings of a massive federal investigation in Beaver, W. Va., suggested the blast was preventable. The federal report said coal dust had been allowed to accumulate, turning a small methane explosion into a large one. Alpha Natural Resources acquired Massey last month. A spokesman said the company is conducting its own investigation.