CHARLESTON, W.Va. -- Still more evidence implies that 29 West Virginia miners were killed because of deliberate safety law violations at Massey's Upper Big Branch mine in Raleigh County over a year ago.

Mine operators "cooked the books," listing safety hazards in private company reports but omitting them from official records seen by federal inspectors, U.S. Mine Safety and Health Administration leaders said Wednesday near Beckley. The deceitful records were countersigned by "upper management" in addition to local supervisors.

Also, Massey intimidated foremen to maximize production at the expense of safety, MSHA indicated. One was fired because he delayed coal output to fix ventilation problems.

Also, dangerous levels of explosive coal dust were allowed to accumulate in the mine, not cleaned up or covered with rock dust to suppress the risk of detonation, as required by law, MSHA reported. (The fact that autopsies found a disturbing three-fourths of the UBB victims had black lung disease implies the presence of too much coal dust.)

Also, water sprays designed to prevent sparks were missing, faulty, clogged or otherwise inoperable.

Also, ventilating systems designed to suck lethal methane out of working sections were botched, half-working. On the day of the explosion, they were flowing backward.

These ugly revelations increase the prospect that significant criminal prosecutions may arise from several ongoing investigations into the 2010 tragedy, the worst U.S. mine disaster in 40 years.

Since the deadly blast, Massey has insisted that an unpreventable act of God -- a sudden inflow of explosive methane gas -- was to blame. But two governmental probes reject that theory.

First a special state investigation, and now the federal MSHA findings, say there's no evidence of excess methane. Instead, it seems likely that a coal-cutting machine hit rock, causing a spark that wasn't squelched by sprays, which produced a small methane blast -- then the jolt caused uncovered coal dust to swirl up into a mammoth explosion.

After MSHA's Wednesday disclosures, United Mine Workers President Cecil Roberts said concealment of hazard reports "confirms that management knew there were serious problems at the mine, yet chose to hide them from safety officials and the miners themselves."

Over the years, the Massey mine racked up a monstrous record of safety violations. It's hard to understand why federal and state inspectors didn't shut down the pit, long before the fatal day.

So far, only two low-ranking UBB employees have been charged with criminal violations. As ominous evidence keeps growing, it's hard to believe that the scope of prosecutions won't increase. Justice seems to require it.