Gary May pleaded guilty to hiding safety violations from inspectors . He has agreed to cooperate with federal investigators . The Upper Big Branch mine blast in 2010 killed 29 workers . Comment:
Gary May pleaded guilty to hiding safety violations from inspectors . He has agreed to cooperate with federal investigators . The Upper Big Branch mine blast in 2010 killed 29 workers . May is the highest-ranking Massey Energy executive to face charges , prosecutor says .