Massey Energy kept two sets of records at the West Virginia coal mine where 29 workers died in an explosion last year, omitting recurring safety problems to mislead government inspectors, a federal official announced today.

"The investigation team concluded that the managers were aware that chronic hazardous conditions were not recorded" at the Upper Big Branch mine, Kevin Stricklin, coal administrator for the Mine Safety and Health Administration, said during a briefing on the federal investigation, the Associated Press reports.

The second set of records was revealed Tuesday night during a briefing to family members of the miners who died in the April 2010 blast.

People who attended the briefing told The Charleston Gazette that one set of records was called the "official" book, which was shown to government inspectors, while the other set was called the "production" book, which noted safety problems or hazards omitted from the "official" record.

Stricklin said top Massey management was required to countersign safety inspection books that collect miners' daily reports on conditions. Testimony from some of the 266 witnesses his agency has interviewed "indicated that management pressured examiners to not record hazards in the books."

Massey sold the mine to a rival, Alpha Natural Resources, this month.

Alpha Natural Resources spokesman Ted Pile told the AP in an e-mail it was just hearing about the faked reports for the first time. "It's a claim I'm sure we'll look into as we conduct our own review of what happened," Pile wrote.