thanks for the comment, there I wrote it.
My interest stems from the point that death at the hands of the local Russian's passing through is the most obvious answer.
My findings were that this was the most least possibility, Berthier was alone in the room when he fell out of the window, there are two theories - suicide and accident.
I am one of the accident believers.
Also in my view Berthier's health was so run down - that he wouldn't be an asset to N any longer, a life time of war had taken its toll.