The first report on the explosion that killed 29 men at West Virginia's Upper Big Branch mine will be released Thursday.
Independent investigator J. Davitt McAteer was appointed by then-Gov. Joe Manchin to examine the 2010 blast at Massey Energy Co.'s mine near Montcoal.
McAteer tells West Virginia Public Broadcasting he will first brief the victims' families on his conclusions.
The report is based on more than 300 interviews. McAteer says it will also address theories put forth by Virginia-based Massey and the federal Mine Safety and Health Administration.
MSHA investigators believe an accumulation of highly explosive coal dust and faulty equipment triggered the blast. Massey denies dust played a role.
The company blames a sudden inundation of methane or natural gas that overwhelmed all safety systems.