In an outcome described as “unprecedented” by a federal prosecutor, former Massey Energy Co. CEO Don Blankenship was found guilty of violating safety regulations at the Upper Big Branch mine in West Virginia, which led to the 2010 explosion that killed 29 workers.

It was a mixed verdict for Blankenship, who could have faced 30 years in prison had he been convicted of the more serious charges involving securities fraud and making false statements.

Nonetheless, federal prosecutor U.S. Attorney Booth Goodwin called Blankenship’s conviction on a misdemeanor charge “a landmark day for the safety of coal miners.” Goodwin said he believes it’s the first time the head of a major corporation has been held responsible for a workplace safety crime.

The conviction for conspiring to willfully violate mine safety standards carries up to one year in prison. He was not found guilty of a more serious conspiracy charge.

Hundreds of safety violations were found at the Upper Big Branch mine after the incident – the worst mining disaster in U.S. history. Blankenship was accused of running Massey Energy as a “lawless enterprise” which dangerously sped up production and ignored safety in order to maximize profits.

"The defense argued the government has produced no direct proof Blankenship was involved in any conspiracy, only reams of paper, referring to the thousands of pages of evidence the prosecution has entered in the case."

While Blankenship is the highest-ranking Massey Energy official to face justice, he is not the only one. Former mine superintendent Gary May admitted to "ordering a company electrician to disable a methane monitor on a mining machine so it could continue to cut coal without automatic shutdowns" in a plea deal that sent him to prison for 21 months.

Another former Massey executive, David Hughart, "admitted to being part of a corporate conspiracy to evade surprise mine safety inspections by giving advance warning to miners underground." Hart was sentenced to 42 months in prison.