The report says:
In an alpine flight, the aircraft struck a ridge violently
mountain on which it stops thereafter.
There would always be a fuel leak anyway - every plane like this will have a few gallons of unusable fuel.
I am no spin specialist but I gather a flat spin results in a relatively low VS. I have read one aero champion saying a flat spin is a reasonable way to descend through cloud if caught above an overcast... In this case the VS was very high.
Twins are not required to be able to recover from a spin,
AFAIK. But I don't think this was a spin.
It almost makes sense that the pilot may have been doing some "amateur aeros" and in a descent into the valley he misjudged it and hit that rock. That would account for it - except for the evidently zero forward speed. In flight, there is no way to translate say 150kt into a VS of say 100-150kt and zero forward speed.