NPR People: Howard Berkes

NPR NEWS INVESTIGATION: The two officials were underground, unsupervised for as long as four hours after the explosion at the Upper Big Branch coal mine in April. Massey Energy says the pair were searching for survivors, but some investigators and experts are concerned they could have tampered with evidence.

Federal regulators vowed to crack down on mine operators who warn miners of inspectors' arrival.

Massey Energy agreed to settlements with four families of dead miners as a criminal probe continued.

U.S. mining experts say Chilean authorities face two daunting tasks as they try to rescue 33 miners trapped underground since Aug. 5: drilling a wide borehole nearly a half-mile down to reach the miners; keeping the miners safe and sane during four months of expected drilling.

Ricky Lee Campbell of Beckley, W.Va., is a central figure in the federal criminal investigation that grew out of the Upper Big Branch mine explosion in April that left 29 mine workers dead.

Federal mine safety officials urged caution in the wake of conflicting reports about the investigation of the April coal mine disaster in West Virginia that left 29 mineworkers dead. Mine owner Massey Energy has tried to present its own theory about the tragedy.

Testing of two methane monitors from the Upper Big Branch coal mine in West Virginia has not detected any evidence of tampering, NPR has learned. The methane monitors were removed from the longwall mining machine believed to be a possible ignition source of the April 5 explosion that killed 29 mine workers.

Investigators have recovered three key pieces of evidence in the explosion that killed 29 mine workers in West Virginia on April 5, NPR has learned. The evidence includes two safety devices that sound alarms and shut down mining machines when methane gas approaches explosive levels. Investigators want to know whether the devices were a factor in the blast.

In a private briefing for families of the victims, company executives also repeated claims that the massive blast that killed 29 mine workers was caused by natural forces.

An information vacuum in the investigation of the deadly mine disaster in West Virginia in April has mine owner Massey Energy suggesting possible causes of the explosion. The latest involves a massive infusion of methane gas before the blast.

In twin assaults Thursday, both Massey Energy and CEO Don Blankenship suggested that an "overwhelming" rush of methane gas may have been the cause of a deadly April 5 explosion at Massey's Upper Big Branch mine in West Virginia. Mine safety officials are skeptical.

Massey Energy CEO Don Blankenship spoke at the National Press Club in Washington on Thursday as his company floated a new theory for the cause of the April 5th explosion that killed 29 mine workers. The theory appears to be the latest attempt by the company to deflect criticism of its own safety practices.

NPR News has learned that a February incident in which a mining machine's methane detector was deliberately disabled was not an isolated incident at the Upper Big Branch coal mine in West Virginia. Miners who worked in the mine say the practice was relatively common and was justified with false descriptions of mining regulations. A methane explosion in April killed 29 workers.

Two months before the explosion in April killed 29 mine workers, three witnesses say an electrician was ordered to disable a methane detector, an NPR News investigation finds. Working without an operational methane monitor is dangerous and potentially illegal.

Federal administrative law Judge L. Zane Gill ruled that there is "substantial evidence to support a reasonable cause to believe" that Ricky Lee Campbell's repeated complaints about dangerous safety problems at another Massey mine prompted his termination.