U.S. Attorney Booth Goodwin said May's admission shows that the obstruction of federal Mine Safety and Health Administration inspectors "was a routine matter at Upper Big Branch.''
A recent internal review by MSHA concluded that federal inspectors either missed problems or failed to examine areas where they existed in the 18 months before the blast. But the review found no evidence those failures caused it.
Last week, though, a team led by the National Institute for Occupational Safety and Health issued a report concluding that timely enforcement of existing regulations "would have lessened the chances of -- and possibly could have prevented'' the explosion.
Alpha Natural Resources of Bristol, Va., bought Massey and all its operations, including the Upper Big Branch mine, last summer.
Prosecutors have refused to say whether they are targeting former Massey CEO Don Blankenship, a hard-nosed executive whose company was cited for violations so frequently that union critics accused him of regarding fines as simply the cost of doing business.
Blankenship, once one of the most outspoken leaders in the coal industry, retired months after the explosion and moved away from West Virginia. A telephone number for him could not be found, and he has all but disappeared from public view since the blast.
"I'm glad to see he pleaded guilty, and I hope it goes up the ladder. I'm not satisfied just with him. I want other people, including Don Blankenship,'' said Jack Bowden, whose son-in-law, Steve Harrah, was among the miners who died.
Defense attorney Tim Carrico declined comment after the hearing.
Former Upper Big Branch security chief Hughie Elbert Stover was sentenced in February to three years in prison for lying to investigators and ordering a subordinate to destroy security-related documents. It's one of the stiffest punishments ever issued in a mine safety case. His attorney, William Wilmoth, is appealing the conviction.
May, 43, has cooperated with prosecutors in the continuing criminal investigation and testified at Stover's sentencing.
"That cooperation is going to be key as this investigation goes forward,'' Goodwin said.