THE ACFT CRASHED AFTER STARTING A GO-AROUND OR ABORTED LANDING AT NORMAL OK. THE ACFT WAS ON A X-COUNTRY FROM DALLAS TO WICHITA. THERE WAS NO RADIO COMMUNICATION WITH THE ACFT AFTER IT WAS CLEARED TO LAND. THE APPROACH LOOKED OK BUT ON SHORT FINAL THE ACFT SUDDENLY TURNED RIGHT, LEVELED THEN ENTERED A STEEP CLIMBING RIGHT TURN AND CONTINUE TO ROLL UNTIL INVERTED THEN PITCHED NOSE DOWN UNTIL CRASHING. THE PLT IN THE RIGHT SEAT HAD REPORTEDLY WORKED LATE THE NIGHT BEFORE INSTALLING WHAT APPEARED TO BE AN AUX FUEL SYSTEM IN THE CABIN. THE ACFT HAD JUST BEEN SOLD AND THE IDENTITY AND LOCATION OF THE OWNER WAS NOT ESTABLISHED. NO ONE CLAIMED THE WRECKAGE. EVIDENCE REVEALED THAT BOTH PROPELLERS WERE ROTATING AT HIGH RPM AT IMPACT. THE FIRE AFTER IMPACT BURNED MOST INTENSELY AND PERSISTANTLY IN THE CENTER OF THE CABIN WHERE THE REMAINS OF WHAT APPEARED TO BE AN AUX FUEL SYSTEM WERE FOUND. NO PRE-IMPACT MALFUNCTONS OR FAILURES WERE FOUND.