An investigation of the possible causes of the explosion was launched on 22 April 2010 by the USCG and the Minerals Management Service.[36] On 11 May the United States administration requested the National Academy of Engineering conduct an independent technical investigation.[307] The National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling was established on 22 May to "consider the root causes of the disaster and offer options on safety and environmental precautions."[308] The investigation by United States Attorney General Eric Holder was announced on 1 June 2010.[309] Also the United States House Committee on Energy and Commerce conducted a number of hearings, including hearings of Tony Hayward and heads of Anadarko and Mitsui's exploration unit.[81][310] According to the US Congressional investigation, the rig's blowout preventer, built by Cameron International Corporation, had a hydraulic leak and a failed battery, and therefore failed.[311]