The Associated Press quoted Wheeling Jesuit University vice-president for sponsored programs and former assistant secretary of the US Mine Safety and Health Administration Davitt McAteer, who is leading a team of investigators at the direction of former governor Joe Manchin, as saying that the group felt “pretty good” about its understanding of the incident and the events leading up to it.

He expected that data from its probe could be released to the families of the victims within the “next month or so”, followed by a review by the governor before public release.

The process, which took nearly a year, included more than 300 interviews with involved parties as the group attempted to determine the events surrounding the explosion last April 5 that killed 29 workers.

"It's important to do, you pick up little nuggets here and there," the AP quoted McAteer as saying.

"There's nobody you can find out there that can give the answer to the whole thing. You get little pieces of information that ties into somebody else's information that ties into somebody else's information, and then you put that together in some sort of picture."

Investigations by other federal agencies, including MSHA, are still ongoing, as is an internal probe by mine owner Massey Energy.

McAteer noted that the only remaining items on his group’s list were a few interviews, some lab tests, and “bits and pieces” of underground investigations.

Over the course of the investigation, a number of factors had slowed the process.

"It's a large, large investigation – physically large," McAteer said.

"The conditions of the mine were such that it made the recovery and the investigation ... more difficult. There were some cases where conditions of the mine wouldn't permit it."

He mentioned that other factors, such as a lack of cooperation by the operator, had left investigators without some of the needed resources.