Could be pilot/copilot sabbatoge. One of them seized controls and maneuvered aircraft in a way that broke it up. The sounds could have been a struggle or stabbing.
But I did hear this aircraft had experienced serious tail damage in a prior incident so mechanical failure remains the most likely cause.
That and the Kenyan
Years back there was a B747 with a repaired pressure patch in the tail section that failed. Plane disintegrated. It was determined that it was a bad repair job.