THE ACFT WAS FLOWN INTO IMC WX AFTER THE FLT HAD BEEN ADVISED BY THE WX SERVICE THAT VFR FLT WAS BARELY FEASIBLE. NO WX BRIEFING BY FAA WAS RECORDED & NO FLT PLAN WAS FILED. THE ACCIDENT OCCURRED DURING THE HRS OF DARKNESS. A WITNESS NEAR THE ACCIDENT SITE OBSERVED AN ACFT THRU BREAKS IN THE CLOUDS WHICH APPEARED TO BE FLYING UNDER CONTROL ON TOP OF THE CLOUDS OR IN BETWEEN LAYERS OF CLOUDS. A LOUD SOUND WAS HEARD AND THE ACFT WAS SEEN TO FALL OUT OF A SOLID UPPER CLOUD LAYER FOR ABOUT 300-500 FT BEFORE DISAPPEARING INTO A LOWER CLOUD LAYER. SEPARATED COMPONENT OF THE LEFT & RT WINGS OF THE ACFT WERE LOCATED OVER A MILE FROM THE MAIN WRECKAGE IMPACT CRATER. THE PLTS LOG DID NOT CONTAIN ANY HISTORY OF HOODED OR INSTRUMENT FLT. NO MEDICAL OR MECHANICAL DISCREPANCIES OF A CAUSAL NATURE WERE FOUND DURING THE POST ACCIDENT INVESTIGATION.