Two months after an explosion on BP's Deepwater Horizon oil rig in the Gulf of Mexico killed 11 people, Panorama's Hilary Andersson tells the story of America's 'greatest environmental disaster.' Dubbed an environmental '9/11' by President Obama, the leak caused by the explosion is still releasing thousands of barrels of crude oil a day into the waters of the Gulf - livelihoods and ecosystems are threatened, fishermen are unable to work and billions have been wiped off the value of BP shares.