THE PLT & COPLT WERE ON A 15-DAY TRIP, WHICH INCLUDED STOPS AT ALL STATE CAPITOLS IN THE CONTERMINOUS UNITED STATES. THE ACDNT OCCURRED ON THE NEXT TO LAST LEG OF THE TRIP. THE PLT WAS ON A VFR FLT, WHEN HE CONTACTED APCH CTL & REQUESTED LANDING INSTRUCTIONS. HE WAS ADVISED THAT IMC CONDITIONS EXISTED AT THE DESTN ARPT. HE THEN OBTAINED VECTORS FOR AN ILS RWY 23 APCH. AFTER ACKNOWLEDGING CLNC TO LAND, THERE WAS NO FURTHER TRANSMISSIONS FM THE ACFT. A WITNESS THAT LIVED NEAR THE FLT PATH TO RWY 23 HEARD THE ACFT & SAW IT FOR ABOUT 2 SECONDS WHEN IT APPEARED IN A BREAK IN THE CLOUDS. SOON THEREAFTER, HE HEARD THE ACFT HIT TREES & CRASH ABOUT 1 MI FM THE APCH END OF THE ARPT AT AN ELEVATION OF ABOUT 1018 FT. WRECKAGE WAS SCATTERED OVER A 600 FT AREA. THE WITNESS RPRTD THE ACFT WAS VERY LOW BEFORE IT CRASHED, BUT THE ENG SOUNDED NORMAL. NO PREIMPACT PART FAILURE OR MALFUNCTION OF THE ACFT WAS FOUND DURING AN INVESTIGATION. DECISION HEIGHT FOR THE APCH WAS 1181 FT.