The federal government has filed charges against a former Massey Energy mine superintendent. Gary May worked at the Upper Big Branch Mine in West Virginia in April 2010, when an explosion killed 29 coal miners. May is charged with felony conspiracy. According to the charges filed today in West Virginia, May is accused to tampering with methane detectors, covering up mine safety violations and falsifying records. May is the second Upper Big Branch employee to face federal charges. The first, former security chief Hughie Stover, set to be sentenced next week.