BLUEFIELD, W.Va. (AP) -- Several workers in a southern West Virginia coal mine knew explosive methane was pouring into the mine just moments before the blast that killed them, according to the mine owner's top executive.There's evidence miners cut off electricity to the cutting head of the Upper Big Branch mine's main mining machine and stopped its coal conveyer, Massey Energy Co. chief Don Blankenship said. Blankenship based his theory largely on photographs taken by federal investigators.Blankenship said they show equipment that was turned off manually by miners. The photos do not indicate why.The revelations are the newest about the April 5 explosion that killed 29 miners and injured two.The blast is the worst U.S. coal mining disaster since 1970 and the subject of civil and criminal investigations.Blankenship's information supports Massey's theory that so much methane flooded the mine so quickly that it overwhelmed safeguards including ventilation equipment that the Virginia-based company argues was weakened by government regulators.Massey suspects the gas poured into the mine through a crack that opened up in the floor. MSHA had investigated two previous inundations at Upper Big Branch."I'm not standing here telling you that the crack caused the gas,'' Blankenship said Tuesday. "I am telling you that in 1997 and 2004 similar incidents occurred and there are cracks underneath the shearer. There are evidence that the crew behaved in much the same manner.''Blankenship showed photographs that he said indicate some of the seven men found dead along the mine's longwall mining machine took steps to shut it off.One showed a switch that requires an operator to push a button while changing it. "The explosion could not have possibly thrown that,'' Blankenship said. "This shows the water valve which also had been cut off, which shows that they had again shut down the wall.''Federal Mine Safety and Health Administration officials have not dismissed the possibility that methane flooded the mine through a crack. But the agency has said the crack identified repeatedly by Massey was not the source of gas in the mine that day.MSHA hasn't determined what caused the explosion, but a preliminary report issued in April identified methane fueled by coal dust was responsible.On Friday, the agency released information that 1,400 of 1,803 samples collected inside the mine by investigators show excessive amounts of coal dust were present before the blast. Massey disputes that evidence, noting that a federal administrative law judge dismissed citations based on similar samples after a 2001 explosion in Alabama.The Associated Press reported Sept. 12 that handwritten logs recording inspections by Upper Big Branch employees showed eight conveyer belts had excessive amounts of coal dust 32 minutes before the explosion.Massey officials insist the mine was properly dusted at the time of the blast.MSHA, however, announced an emergency rule Tuesday to require underground mines to do more to control coal dust.