AFP: Oil giant BP revealed Friday it has so far spent 5.1 billion pounds to battle the Gulf of Mexico disaster, as its crews worked to retrieve key evidence from the seabed. Robotic submarines recorded the delicate operation as engineers sought to raise a failed blowout preventer from the sunken rig to the surface and hand it over to the US Justice Department. The US government is conducting what could be a criminal investigation into the April 20 explosion and subsequent oil spill …