An investigation into the Deepwater Horizon rig explosion has uncovered new evidence that BP was aware of problems aboard the rig prior to the April 20 blowout that killed eleven workers, destroyed the rig, and launched the worst US oil spill. A BP employee testified Tuesday that Deepwater Horizon’s blowout preventer had a leak in the days before the explosion, but BP did not comply with a federal regulation requiring the rig to suspend operations. In addition, the Houston Chronicle reports Halliburton warned BP two days before the deadly accident that it could have a severe problem with natural gas escaping from the well. The ongoing investigation has also revealed that a September 2009 audit by BP identified 390 maintenance projects aboard the rig that were past due.