AFTER DEPARTING ON AN INSTRUMENT FLIGHT, THE PILOT REPORTED A SYSTEM PROBLEM AND REQUESTED CLEARANCE BACK TO THE DEPARTURE AIRPORT. SOON THEREAFTER, THE PILOT DECLARED AN EMERGENCY BECAUSE HE WAS EXPERIENCING A GYRO PROBLEM. NO FURTHER COMMUNICATION WAS RECEIVED FROM N6858V. INSTRUMENT WEATHER CONDITIONS PREVAILED AT THE TIME OF THE ACCIDENT. WITNESSES HEARD THE AIRPLANE FLYING IN CLOUDS BEFORE IT CRASHED. REPORTEDLY, IT MADE AN 'S' TURN, THEN IT WAS OBSERVED BELOW THE CLOUDS, SECONDS BEFORE IMPACT. THE AIRPLANE WAS EXTENSIVELY DAMAGED DURING IMPACT. AN EXAM OF THE FLIGHT CONTROLS FAILED TO DISCLOSE ANY OBVIOUS MALFUNCTION OR CONTROL FAILURE. EXAMINATION OF THE ELECTRICAL COMPONENTS AND VACUUM SYSTEM COMPONENTS FAILED TO INDICATE A MECHANICAL PROBLEM. BOTH GYROS SHOWED SIGNS OF ROTATION, AND THE VACUUM PUMP SUSTAINED IMPACT DAMAGE. A LOW LEVEL OF ETHANOL WAS DETECTED IN THE PILOT'S LIVER TISSUE, BUT NONE WAS FOUND IN KIDNEY TISSUE.