THE ACFT, AT NEAR GROSS WEIGHT (CG UNKNOWN), WAS ON INITIAL CLIMB AFTER TAKEOFF. A WITNESS REPORTED THAT ENGINES SOUNDEDNORMAL. AT ABOUT 400 FT AGL THE ACFT WAS REPORTED TO PITCH UP ABOUT 10 DEGREES, THEN LEVEL OFF AND ENTER A LEFT TURN. THE ACFT MADE ANOTHER LEFT TURN TO THE SSW. THE PILOT RPRTD THAT HE WAS RETURNING TO THE FIELD, BUT DID NOT STATE PROBLEM. THE WITNESS SAID THE ACFT WAS IN A 30 DEGREE LEFT BANK, TURNING TOWARD THE ARPT, WHEN THE ACFT STALLED AND DESCENDED TO THE GND IN A VERTICAL NOSE DOWN ATTITUDE. FIRE/EXPLOSION AFTER IMPACT. LEFT PROP FND IN FEATHERED POSITION.NO ENGINE PROBLEM FOUND. ON 1/28/87, LT ENGINE LOST POWER AFTER TKOF; NO PROBLEM FOUND; UNABLE TO DUPLICATE. PLT HAD 2 ENGINE-OUT EXPERIENCES IN AIRPLANE PREVIOUSLY, BOTH WHEN AT LOW WEIGHT. SURROUNDING TERRAIN SUITABLE FOR OFF-AIRPORT LDG.