At 8:52 p.m. on April 20, 2010, exactly 57 minutes before the Deepwater Horizon oil rig exploded, the top BP man onboard called an engineer in Houston to say he didn't understand the results of a test that would tell them whether the well had been properly sealed. What Donald Vidrine said he was seeing should have caused him to shut the project down, an expert witness for the government has testified in a court deposition. Mark Hafle, the engineer in Houston, told Vidrine something wasn't right. But instead of stopping operations or investigating further, Vidrine concluded -- apparently by the end of the phone call -- that it was safe enough to remove the well's drilling mud, the last barrier against a blowout.