What caused the 2006 Sago mine disaster that killed 12?

WHAT CAUSED THE 2006 SAGO MINE DISASTER THAT KILLED 12?
Numerous theories have been offered:
* The United Mine Workers of America, in a study released in March, blames the company and state officials.
* The study argues that frictional activity, poor maintenance and lax state regulations are to blame.
* International Coal Group Inc, the company that operated the Sago mine, advanced the theory that lightning caused the explosion.
* A study commissioned by West Virginia Governor Joe Manchin does not address the cause.
Source: United Mine Workers of America, the International Coal Group Inc., West Virginia Governor's office.