By Vicki SmithThe Associated PressMORGANTOWN, W.Va. -- The Mine Safety and Health Administration on Monday asked a federal judge to dismiss a lawsuit over its plan to privately interview witnesses in a deadly April coal mine explosion, arguing no outside party has the right to control or direct investigations.In filings with the U.S. District Court in Beckley, MSHA and agency director Joe Main also argue the court lacks jurisdiction to rule on the demands made by the United Mine Workers of America and the families of two miners who were among 29 men killed at the Upper Big Branch mine in Montcoal.The UMW is participating in the investigation as a representative of some miners, even though the accident occurred at a nonunion mine owned by Virginia-based Massey Energy.The union and relatives of miners William Griffith and Ronald Maynor want a court order allowing them to observe the interviews MSHA is conducting with witnesses, but Main argues in a memorandum with the motion to dismiss that they have no legal foundation for such a demand.MSHA is not using its subpoena power to compel testimony. Rather, it's seeking "sworn voluntary testimony from willing participants.'' The plaintiffs, the agency argues, "are at liberty to do the same.''The agency has previously said a combination of private interviews and public hearings will protect the integrity of the investigation and the confidentiality of witnesses without impeding a criminal investigation that's also under way.The plaintiffs are not being denied participation to the process, just the interviews, MHSA contends. They will be entitled to copies of the witnesses' statements later and can use them as evidence in lawsuits.The April 5 blast was the nation's worst coal mining disaster in 40 years. While federal regulators have identified highly explosive methane gas, coal dust or a combination of the two as the likely cause, the ignition source remains unknown.MSHA's response also says the lawsuit makes "entirely unsupported assumptions'' about what investigators will explore during the private interviews and essentially asks the court to assume the investigation will be a failure.MSHA also notes that if the demands of the UMW and the families were granted, Massey would likely want equal access. Allowing so many people to participate in the interviews raises the risk that witnesses will be less candid and that they could be subject to intimidation or retribution, the agency says."Subordinating MSHA's investigative powers to private interests would be disastrous to the investigative process and make a mockery of Congress' mandate to MSHA,'' it said.No hearing dates have been set in the lawsuit.