N5527K CRASHED ABOUT 2 MILES SOUTH OF THE ORANGE CNTY AIRPORT SHORTLY AFTER A NIGHT TKOF FM RUNWAY 21. DEPARTURE INSTRUCTIONS FOR THE IFR FLT INCLUDED A RIGHT TURN OF 130 DEGREES, TO 340 DEGREES MAGNETIC TO INTERCEPT V-58 AND CLIMB TO 5000 FT. THE PLT CONTACTED BOSTON ARTCC, APPARENTLY AFTER TKOF. WHEN ASKED IF HE WAS AIRBORNE THE RESPONSE FM THE PLTWAS GARBLED. THERE WERE NO FURTHER RADIO TRANSMISSIONS AND RADAR CONTACT WAS NOT ESTABLISHED. WITNESSES RPTD HEARING A LOW FLYING ACFT BUT DID NOT SEE IT. THEY RPTD MISTY/FOGGY WEATHER CONDITIONS. A PARTIAL OBSCURATION WITH A CEILING OF 1000 FT OVCST, 4 MILES VISIBILITY, FOG AND HAZE WAS RPTD 7 MILES EAST OF THE ACDT SITE. THE ACFT IMPACTED IN A STEEP DESCENT. DESTRUCTION OF THE ACFT PRECLUDED DETAILED SYSTEMS DOCUMENTATION. ENGINE TEARDOWNS DID NOT REVEAL EVIDENCE OF MECHANICAL MALFUNCTION OR FAILURE. TREE LIMBS OVER CRASH SITE WERE BROWN-STAINED AS IF BY FUEL.