THE ACFT CRASHED IN THE OCEAN NR DUNCAN TOWN, BAHAMAS. THE WX ACCORDING TO WITNESSES WAS VMC. THE FLT HAD BEEN AIRBORNE ENROUTE FROM NASSAU FOR ABOUT 1 HR AND 20 MINUTES. WITNESSES ON A NEARBY BOAT SAID THE ACFT WAS FLYING IN A SLIGHT LEFT BANK WHEN THE LEFT WING SEPARATED FROM THE ACFT. THE ACFT ROLLED TO THE LEFT AND IMPACTED THE WATER. THE WRECKAGE SANK WHERE THE WATER WAS ABOUT 50 FT DEEP. THE LEFT OUTBOARD WING PANEL WAS RECOVERED AND EXAMINED AT THE NTSB LAB. ALL FRACTURES WERE FOUND TO BE FROM OVERSTRESS. NO PREEXISTING CRACKS WERE FOUND AND NO EVIDENCE OF FATIGUE OR FAILURE FROM CORROSION. THE WING TIP HAD CRUSHING DAMAGE AND A BLUE PAINT TRANSFER AS IF FROM A COLLISION. THE PARTLY BLUE VERTICAL STAB WAS DAMAGED FROM THE SEPARATED WING SECT STRIKING IT. THE WX REPORTED EN ROUTE WAS: BROKEN TO OVERCAST WITH RAIN SHOWERS AND ISOLATED THUNDERSTORMS. EXAM OF THE LATER RECOVERED INBOARD LEFT WING SECTION SHOWED SEPARATION OF THE OUTBOARD WING SECTION RESULTED FROM OVERSTRESS.