JEFFREY BROWN: Finally tonight, new findings and charges in the investigation of the Upper Big Branch Mine disaster in West Virginia. It was the deadliest in the U.S. in four decades—29 men were killed on April 5, 2010, after an explosion at the mine then owned by Massey Energy.

Today, state mining officials issued 253 violations against the company and released their final report. In it, they singled out two foremen, saying they repeatedly failed to clean conveyor belts or apply rock dust used to neutralize explosive coal dust, all leading to unsafe conditions.

And, just yesterday, federal prosecutors brought criminal fraud charges against the mine's former superintendent Gary May.

Now we walk through the latest with NPR's Howard Berkes.

He's been covering this story since the accident.

Howard, welcome to you.

So now we have this new state report. Is the picture fairly clear now on what happened that day? Walk us through what we know.

HOWARD BERKES, National Public Radio: Sure.

The state report didn't really add much to what we already knew, which was that this was a mine that was operated in a way that there was ignoring of fundamental safety operations, that safety procedures were flawed at that mine, that equipment didn't work properly, and that the management of the mine was more oriented to production than safety.

The state pretty much repeated what the early investigative reports have said, that this was caused by a methane ignition, that water sprayers were not functioning and failed to control methane gas, that there wasn't enough ventilation in the mine to control methane gas, and that that coal dust that you mentioned, there was so much of it, that a small, relatively small methane gas ignition exploded into this massive explosion that coursed through the mine because of the presence of all that coal dust.

JEFFREY BROWN: So, these—these charges of—against—findings about the foreman, I mean so it's a kind of systemic failure rather than a particular incident. And I gather the state is limited in what it can do at this point?

HOWARD BERKES: Well, it's interesting that in that state report, they noted that the maximum fine for those foremen, for these citations, is $250, and that state law doesn't permit citing anyone above the level of mine foreman.

And those foremen didn't make up the way that they behaved in that mine. They were working at the direction of a mine superintendent, of the president and vice president of the Massey Energy subsidiary that ran that mine. And we know from documents that have been released in the investigation so far and in a deposition by former CEO Don Blankenship in another case that this mine was micromanaged and that Blankenship and other senior officials at Massey Energy knew what was going on there.

They monitored the coal production by the foot and by the minute. And so, even though it's clear that these—that the superintendent who was charged yesterday and that the mine foremen who were mentioned in the state report today were not acting on their own, it appears that it's very difficult in—certainly in state law in West Virginia to reach beyond the foreman to cite anyone else and get anyone else held responsible.

JEFFREY BROWN: Well, so tell us a little bit more about the federal side of this and that foreman Gary May. So, he's the highest official charged to this point.

What does that tell you? Is he cooperating at this point, or this a way to get to some of the higher-ups?

HOWARD BERKES: It certainly looks that way, based on the way this—these charges were filed.

Gary May wasn't indicted. He was charged in a criminal information. And federal prosecutors use a criminal information when the defendant is cooperating and when they're trying to get testimony against higher-level officials. He was superintendent of the mine, or one of two superintendents of that mine.

And he was responsible for day-to-day operations for portions of that mine. But, again, he was somebody who was working at the direction of higher-level people at the subsidiary company that operated that mine and Massey Energy. He's not somebody who invented the—a way to operate that mine. He was working at their direction.

And so all indications are—prosecutors won't say this directly, but they hint that Gary May is cooperating and that they're working through him to get to higher-level officials.

JEFFREY BROWN: Well, so, finally, Howard, I know you've spent some time with families of miners. What do you hear from them these several years later?

HOWARD BERKES: They're still grieving deeply for their losses as if it just happened yesterday.

But they're encouraged by the fact that the U.S. attorney in the Southern District of West Virginia has filed this charge against Gary May. They're encouraged by the idea that they're trying to reach higher into the upper management ranks of Massey Energy.

And what they say to me over and over and over again is that justice won't be done here until somebody goes to jail. And if somebody does go to jail, it will be rare. And if somebody at a high level goes to jail, it will be even rarer.

Mining company officials don't go to jail for killing coal miners. It rarely happens. Prosecutors seem to be working with a way of trying to get at higher-level officials. And I know families will be relieved and feel that justice has been done if higher-level officials are charged.

JEFFREY BROWN: All right, Howard Berkes of NPR, thanks so much.

HOWARD BERKES: Thanks for having me.