THE HOME ARPT FOR THE ACFT WAS AT MONROE, LA. THE COMPANY PLT (PIC) & ANOTHER PLT (CP) TOOK THE ACFT WITHOUT COMPANY AUTHORIZATION. THEY FLEW TO RUSTON, LA (APRX 30 MI WEST OF MONROE) & PURCHASED FUEL, ALTHOUGH FUEL WAS AVAILABE AT THE HOME ARPT AT A SOMEWHAT HIGHER PRICE. AT RUSTON, THE PIC TOLD AN ACQUAINTANCE THAT HE WOULD BE RTRNG TO MONROE IN A 'ROUND ABOUT FASHION.' AT 1650 CST, THE ACFT WAS OBSERVED TO DEPART RUSTON IN A NORTHEASTERLY DRCTN. SUBSEQUENTLY, IT CRASHED APRX 60 MI NORTHEAST OF RUSTON (37 MI NORTH-NORTHEAST OF MONROE). AN INVESTIGATION REVEALED THE ACFT HIT TREES & CRASHED ON A NORTHWESTERLY HDG. THE WRECKAGE WAS SCATTERED IN EXCESS OF 300 FT ON HEAVILY WOODED TERRAIN. NO PREIMPACT PART FAILURE OR MALFUNCTION OF THE ACFT OR ENGS WAS FOUND. WX IN THE AREA WAS ESTIMATED TO BE ABOUT 500 FT OVERCAST, VIS 2 MI WITH FOG & LIGHT DRIZZLE. THE ACDNT WAS ESTIMATED TO HAVE OCCURRED AT APRX 1755 CST. OFFICIAL SUNSET AT THE ACDNT SITE WAS 1754 CST.