THE PILOT HAD LANDED AT A CLOSED AIRPORT EN ROUTE TO HIS DESTINATION. HE TOLD WITNESSES AT THE AIRPORT THAT THERE WERE THUNDERSTORMS AT HIS DESTINATION, AND THAT WAS WHY HE DECIDED TO STOP. HE THEN REBOARDED THE AIRPLANE AND DEPARTED. SHORTLY THEREAFTER, THE AIRPLANE WAS OBSERVED FLYING AT ABOUT 100 FEET AGL IN AN AREA ABOUT 5 MILES NORTH OF THE CLOSED AIRPORT. WITNESSES WHO WERE IN A VAN STATED THAT THEY OBSERVED THE AIRPLANE DROP BELOW A TREE LINE AND THEN REAPPEAR. AS THE AIRPLANE PASSED PARALLEL TO THE VAN, IT WAS OBSERVED TO ENTER A STEEP RIGHT TURN AND THEN NOSE DOWN INTO THE GROUND. NO EVIDENCE OF MECHANICAL FAILURE OR MALFUNCTION WAS FOUND. THE PILOT'S CERTIFICATE HAD BEEN ISSUED UNDER AN ALIAS WHICH THE DEA AND CUSTOMS SERVICE SAID THE PILOT HAD USED OVER THE YEARS. THE PILOT'S TOXICOLOGY STUDY INDICATED 0.32 MILLIGRAMS PER LITER OF METHAQUALONE (QUAALUDE) IN HIS LIVER TISSUE.