The FBI has been asking miners whether a supervisor at the Upper Big Branch mine made unauthorized changes to the underground coal mine's ventilation plan and if they had ever disabled methane detectors, the Pittsburgh Post-Gazette reported Tuesday.
Families of the miners killed April 5 have asked the federal Mine Safety and Health Administration to open all investigation reviews to the public.
A missing page in the ventilation plan was first publicly disclosed in a lawsuit against the mine administration by the two of the dead miners' families. The missing page could have noted when mine personnel checked ventilation fans, the Post-Gazette reported.
The Upper Big Branch mine reportedly had been cited for ventilation problems. Massey Energy, which owns the mine, said it did not believe the missing page was "a focus of concern."