Timeline of events in deadly blast at Upper Big Branch mine

Former Massey Energy CEO Don Blankenship was set to be released Wednesday from an Arizona halfway house, marking the end of his one-year prison term for to his criminal conviction in the April 2010 explosion that killed 29 men at the Upper Big Branch Mine in West Virginia.

Four investigations into the disaster found that worn and broken cutting equipment created a spark that ignited accumulations of coal dust and methane gas at the underground mine in Montcoal. Broken and clogged water sprayers allowed what should have been a minor flare-up to become an inferno.

Here is a timeline of major events in the Upper Big Branch disaster:

— April 5, 2010: A huge explosion ripped through the underground corridors of the Upper Big Branch mine, killing 29 men in the worst U.S. coal mining disaster in 40 years.

— April 25, 2010: In a eulogy, a somber President Barack Obama told the families of the workers that the nation would honor their memories by improving safety in the mines.

— May 14, 2010: Federal prosecutors announce criminal investigation.

— Dec. 3, 2010: Don Blankenship, CEO of Upper Big Branch owner Massey Energy, announces his retirement.

— Jan. 29, 2011: Massey Energy agrees to be taken over by Alpha Natural Resources in a $7.1 billion deal.

— Sept. 22, 2011: Former Massey employee Thomas Harrah is sentenced to 10 months in prison for faking a foreman's license and lying to federal authorities.

— Dec. 6, 2011: In the biggest settlement ever reached in a U.S. mining disaster, Alpha Natural Resources agrees to pay $210 million to compensate grieving families, bankroll cutting-edge safety improvements and pay for years of violations by Massey Energy. Under the deal with federal prosecutors, Alpha is not criminally charged.

— Feb. 29, 2012: Former mine security chief Hughie Elbert Stover is sentenced to three years for lying to investigators and ordering a subordinate to destroy security-related documents.

— Jan. 17, 2013: Former Upper Big Branch superintendent Gary May is sentenced to one year and nine months in prison on charges he defrauded the government through his actions at the mine, including disabling a methane gas monitor and falsifying records.

— Sept. 10, 2013: Former Massey executive David Hughart is sentenced to 3 1/2 years in prison for conspiring in an illegal scheme to warn miners and other subsidiaries of surprise safety inspections. Hughart implicated Blankenship in the conspiracy during his plea hearing.

— Nov. 13, 2014: Federal prosecutors announce an indictment against Blankenship.

— Oct. 1, 2015: Blankenship's trial opens in Charleston.

— Dec. 3, 2015: A federal jury convicts Blankenship of a misdemeanor count of conspiring to willfully violate mine safety standards and acquits him of felony charges.

— April 6, 2016: Blankenship is sentenced to one year in prison and fined $250,000.

— May 12, 2016: Blankenship reports to a California prison.

— Oct. 5, 2016: Blankenship declares himself an "American political prisoner" on his blog and announces plans to distribute 250,000 copies of the 67-page manifesto in booklet form.

— Jan. 19, 2017: The 4th U.S. Circuit Court of Appeals in Richmond, Virginia, affirms Blankenship's conviction.

— March 27, 2017: Blankenship is moved to a halfway house in Phoenix, Arizona.

— May 10, 2017: Blankenship scheduled to be released from halfway house.