Two and a half months after an explosion trapped and killed 12 men inside the Sago Mine, their colleagues headed back underground Wednesday and restarted the coal mining operation once again.

The explosion had caught the first crews returning to work after the New Year's holiday Jan. 2. When searchers reached the miners two days later, only one man was still alive.

Although it cannot fully explain what happened, International Coal Group Inc. officials said Tuesday they believe electricity from above — likely a lightning strike — found some conduit into the earth and sparked methane gas that had accumulated in a sealed-off chamber.

It was "unpredictable and highly unusual" and ordinarily hard to prove, said CEO Ben Hatfield.

ICG's investigation of the blast found what Hatfield believes is compelling evidence from three different clocks in three different locations.

At 6:26 a.m., professional weather watchers confirmed an unusually large lightning strike near the mine, he said. Some 70 miles away in Morgantown, a U.S. Geological Survey station confirmed a seismic event at Sago. And deep inside the mine, atmospheric alarms sounded, signaling the carbon monoxide that comes with fires and explosions.

The explosion killed one miner immediately and trapped the crew some 260 feet underground for more than 41 hours. By the time rescue teams reached them, all but one had perished in the poisoned air.

The lone survivor, Randal L. McCloy Jr., was in a coma for weeks and is still recovering from brain damage, but he was well enough Tuesday to leave his Morgantown rehabilitation hospital for a short trip home to Simpson. He has movement in most of his body and is learning to speak again, though doctors say it may be three to six months before he is able to carry on a normal conversation.

Hatfield said ICG's investigation is not the final word on the explosion but he is confident a joint federal-state investigation will reach a similar conclusion.

Gov. Joe Manchin, a constant presence during the disaster, did not immediately weigh in on the company's findings and a spokeswoman said it would be premature to discuss them until the state-federal probe is finished.

Tony Oppegard, a former MSHA official, said he also wants to see the final ruling from federal investigators.

"If, in fact, that is the cause, that doesn't end the inquiry in terms of the company's liability," said Oppegard, now a Kentucky lawyer who represents coal miners in injury cases. "It's a frequent refrain when there's an accident to call it an act of God."

LuluBelle Jones, whose son Jesse died at Sago, said she was not surprised to hear lightning was the likely cause. "It's what we thought," she said.

Although the Mine Safety and Health Administration had cited the mine for 208 violations in the months leading up to the accident, Hatfield said the company's findings show that none of those violations was related to the blast.

The explosion was in a chamber behind 40-inch-thick seals designed to withstand 20 pounds per square inch of pressure — the seals were pulverized by forces the company believes were at least three times that.

Hatfield told The Associated Press late Tuesday that ICG will no longer install seals at Sago and will ventilate existing sealed areas with boreholes to the surface. In time, the company hopes to adopt a technology used in some other mining countries — pumping nitrogen into the abandoned areas to make the gases inert.

"We will not be constructing seals until we can be absolutely certain that an explosive environment is not being created," he said.

The mine was shut down to allow the dangerous gasses to clear out and then for the investigation and safety inspections. On Wednesday, miners returned to work around 6 a.m. and coal was moving out of the mine a few hours later.

ICG bought the Sago Mine near Buckhannon from bankrupt Anker West Virginia Mining Co. last March. The operation has been producing coal since September 1999 and had 145 employees at the time of the accident.