NEW ORLEANS (AP) — Federal prosecutors say a former BP engineer was arrested last week because they feared he would leave the country for a job in Australia and not return.The engineer pleaded not guilty Thursday to charges he deleted text messages to a supervisor and a contractor to prevent them from being used in a federal grand jury probe of the 2010 oil spill in the Gulf of Mexico.Assistant U.S. Attorney Richard Pickens said 50-year-old Kurt Mix of Katy, Texas, applied for a green card to Canada as recently as March and planned to travel to Australia "never to return."Mix faces two counts of obstruction of justice — the first criminal charges in the Justice Department's investigation of BP case.