WASHINGTON (CNN) -- A Senate subcommittee probing this summer's deadly Utah mine disaster has subpoenaed the mine's co-owner, ranking member Sen. Arlen Specter said Friday.
Bob Murray was the outspoken face of the rescue operation at Utah's Crandall Canyon mine.
The subpoena for Bob Murray -- CEO and president of Murray Energy Group -- directs him to appear before the Appropriations Subcommittee on Labor, Health and Human Services on December 4.
Murray Energy operates the Crandall Canyon mine, where six miners were entombed in an August 6 collapse.
Efforts to reach them were suspended 10 days later, when two rescuers and a federal mining official were killed and six others were hurt in a second collapse as they tried to reach the area where the miners were working.
"We're going to get to the bottom of what went on there," said Specter, R-Pennsylvania.
"Murray is an indispensable witness, and, candidly, he really flouted the authority and responsibility of the United States Senate to have his testimony to find out what happened so we could do our utmost to prevent future occurrences."
Murray failed to appear at a September 5 subcommittee hearing on the incident, Specter said.
At the time, Specter and committee chairman Sen. Tom Harkin, D-Iowa, "stressed the importance of Murray's testimony to preventing future mine disasters and indicated they would subpoena the mine owner if necessary."
The subcommittee convened off the Senate floor last month to authorize the subpoena, "an unprecedented event" in its history, Specter said.
Throughout the efforts to reach the miners, Murray said that a small earthquake caused the collapse.
But seismologists said it was more likely that the collapse itself registered as a 3.9-magnitude quake on seismographs.
Last month, relatives of the dead miners told the House Committee on Education and Labor that the men were concerned about safety in the mine, but were afraid to push too hard out of fear of losing their jobs.
Murray Energy valued "production over safety," said Cesar Sanchez, brother of miner Manuel Sanchez.
Steve Allred, brother of miner Kerry Allred, said miners at Crandall were involved in "retreat mining" -- a dangerous practice in which thick pillars of coal holding up the roof of a mine are destroyed in efforts to dislodge more coal.
Murray conceded after the collapse that retreat mining had been done at Crandall, but said the practice was not being used at the time of the cave-in.
Family members of the dead miners have also accused the Mine Safety and Health Administration of not being vigilant enough about regulating the coal mining industry and of failing to keep families informed after the disaster, allowing Murray to take the lead for several weeks. E-mail to a friend