DURING A PART 135 ON-DEMAND AIR TAXI CARGO FLT, THE PLT REPORTED AN ENG MALFUNCTION WHEN THE ACFT WAS APRX 15 MILES SW OF THE ARPT WHILE ON APCH TO LAND. THE FLT CONTINUED & THE PLT THEN REPORTED THAT THE ENG QUIT & THE FLT WAS 5 MILES SW OF THE ARPT. A SEARCH & RESCUE HELICOPTER WHICH HAD JUST LANDED AT THE ARPT FLEW TOWARDS THE ACFT TO OFFER ASSISTANCE, & DUE TO THE DARK NIGHT CONDITION SPOTTED & GUIDED IT TOWARDS A SUITABLE LANDING LOCATION. WHILE DESCENDING THE ACFT FLEW BETWEEN TWO TREES WHICH SEVERED A 1 1/2 FT SECTION OF EACH WINGTIP. AS THE ACFT CONTINUED THE LEFT WING COLLIDED WITH A TREE. THE ACFT SPUN TO THE LEFT AND COLLIDED WITH TERRAIN. AFTER THE PLT EVACUATED THE ACFT, IT WAS CONSUMED BY POSTCRASH FIRE. POSTCRASH EXAM OF THE ENG REVEALED THAT IT SEIZED DUE TO OIL EXHAUSTION. NO DETERMINATION COULD BE MADE AS TO THE REASON FOR OIL EXHAUSTION. EVIDENCE OF OIL LEAKAGE WAS FOUND ON THE FUSELAGE BUT NO SOURCE OF THE LEAK WAS FOUND. THE OIL FILLER CAP WAS FOUND PROPERLY SECURED.