 What actually happened is still uncertain.There was speculation that the aircraft had been shot down by a Soviet S-75 Dvina (NATO designation "SA-2 Guideline") surface-to-air missile, but the official statement by the USAF was that the aircraft was on its third pass along its route when it deviated from its flight plan, orbiting and spiraling down to below minimum radar tracking altitude, indicating that the aircraft crew had probably perished from an oxygen system failure.Although searches for the wreckage continued until 28 December, only small bits and pieces of it were recovered, although unsubstantiated reports asserted that the two crew members had been captured alive by the Soviets.