An autopsy was probably not an option. Don't believe all that you see when you are watching CSI.
I recently spoke with a pilot whom shared a cold one with the pilot a few weeks before the accident. It was stated that the pilot believe it or not, had little outback flying experience under NVFR. It seems like a coincidence that this was discussed, however this outback trip was discussed as it was upcoming as the pilot he was talking to sometimes operates out of the Marree area. Either way the full reason may never be known and the logbooks could quickly disprove this.