CHARLESTON, W.Va. -- Federal prosecutors on Thursday moved to drop one of three felony charges against the security chief at Massey Energy's Upper Big Branch Mine, just four days before opening arguments are set to begin Monday.The move leaves standing allegations that Hughie Elbert Stover lied to investigators and tried to cover up evidence in the probe of the April 2010 explosion that killed 29 miners at Upper Big Branch.Prosecutors allege that Stover told investigators Massey had a policy to never warn workers underground when government inspectors showed up at Upper Big Branch, when Stover himself allegedly directed and trained company security guards to alert workers to impending inspections.Dropping one of the charges allows prosecutors to attempt to prove that Stover lied in a transcribed interview, and not in an unrecorded interview with FBI agents and other government agents."It was a strategic decision in advance of trial," said U.S. Attorney Booth Goodwin.Bill Wilmoth, a lawyer for Stover, could not be reached for comment Thursday evening.U.S. District Judge Irene C. Berger had not yet ruled Thursday on the motion by Assistant U.S. Attorney Blaire Malkin to drop one of the three charges against Stover.Berger and lawyers in the case are scheduled to begin choosing a jury in federal court in Beckley today, and opening statements are expected to start on Monday.Stover is one of two people charged criminally so far in a sprawling federal criminal probe of Upper Big Branch. The April 5, 2010, explosion was the worst U.S. coal-mining disaster in nearly 40 years.Last month, Berger sentenced former Upper Big Branch miner Thomas Harrah to 10 months in jail. Harrah pleaded guilty to faking a foreman's license when he performed key mine safety examinations at the mine between January 2008 and August 2009 and to then lying to investigators about his actions.Originally, Stover was charged in March in a two-count indictment alleging that he lied to FBI agents and U.S. Mine Safety and Health Administration officials and then tried to destroy thousands of pages of security documents that investigators believed could shed light on how Massey handles inspection warnings.In May, Stover was charged with a third count, this one alleging that he also lied to MSHA investigators conducting the civil investigation of the disaster. The original indictment was based on testimony of FBI and MSHA agents, while the additional charge drew on a formal interview taken down word-for-word by a court reporter.Prosecutors are seeking to drop one of the original two counts, involving allegations that Stover lied to the FBI and MSHA during an unrecorded interview in January.The government alleges that Stover initially lied about inspection warnings during a transcribed interview in November 2010 with a civil investigation team composed of MSHA officials, state inspectors and special investigator Davitt McAteer.If convicted of the two remaining charges, Stover would still face up to 25 years in prison.Reach Ken Ward Jr. at firstname.lastname@example.org or 304-348-1702.