Did any locals see any large birds in that area which may have caused a crash, or may have caused a medical incident if there had been a strike?
Birds do not normally fly in fog.
One thing from the "perfect witness" testimony posted earlier; it is not because he could not see the helicopter above him that it was IMC in fog. It could have been above it, VMC , and the hill side could have been obscured ( Mt Erebus syndrome for those old enough to remember)