THE ESTIMATED TIME OF TAKEOFF WAS ABOUT 1930 EST. THE ROUTE OF FLT BEFORE 2000 EST WAS NOT KNOWN. AT APRX 2005, THE PLT REPORTED THAT HE WAS UNSURE OF HIS POSITION. SHORTLY AFTER THAT, THE ACFT WAS IDENTIFIED OVER A MILITARY FIRING RANGE. THE PLT WAS VECTORED FROM THE RANGE TOWARD OCEAN ISLE, NC. AT 2052, THE PLT ACKNOWLEDGED INSTRUCTIONS TO CHANGE TO MYRTLE BEACH APCH CONTROL FREQ, BUT HE DID NOT CONTACT APCH CONTROL. SUBSEQUENTLY, A FEMALE PASSENGER RADIOED THAT THE PLT WAS UNCONSCIOUS & THAT THEY WERE LOST. ATC & THE PLT OF ANOTHER ACFT TRIED TO ASSIST, BUT THE PASSENGER WAS EXTREMELY EXCITED & COMMUNICATION WITH HER WAS VERY DIFFICULT. THE PLT OF THE OTHER ACFT THOUGHT HE HEARD A MALE VOICE IN THE BACKGROUND STATE 'GIVE ME SOME AIR.' SUBSEQUENTLY, THE ACFT CRASHED (AT NIGHT) WHILE IN A STEEP NOSE DOWN. SLIGHTLY INVERTED, R WING LOW ATTITUDE. TOXICOLOGICAL TESTS SHOWED THAT THE PLT & 3 PASSENGERS HAD THE FOLLOWING CARBON MONOXIDE LEVELS: 24%, 22%, 35% & 44%. THE EXACT POSITION OF A CARBON MONOXIDE LEAK WAS NOT FOUND.