I was flying VFR SEP in Switzerland on the day of the accident, I'm based and was flying in the eastern part but have a good look at the weather and particularly winds for the whole of the country before taking off.
There was the usual mist over the 'plateau' that morning but around Sion and over the Alps it was 'grand beau'. Winds were SSW 15-20Kt between 8,000 and 13,000ft.
The accident site is a ridge above the Pont de Forcletta at around 3000m or 9500ft.
The aircraft was based at Geneva, it flew to Lausanne, picked up the 4 passengers and departed for its sightseeing flight. The pilot apparently intended to land after this at Sion.
The accident site is outside the Sion CTR/TMA in Class E, the pilot would not have had to be in contact with any ATC unit but might have been in contact with Geneva Information.
I flew the Baron in 1970-71 at Hamble but never at high altitude with 5 on board. I would think that the aircraft was above its single engine service ceiling, however it looks as though the aircraft impacted vertically with zero forward speed. I would speculate on pilot incapacitation followed by stall and spin.
There don't appear to have been any witnesses, I would think that the flash memories of any installed GPS set and passenger cameras will yield important clues.