DRG TAKEOFF, THE BAGGAGE DOOR (BD) CAME OPEN. TWR PSNL ADVISED THE PLT, BUT RECD NO DISCERNIBLE REPLY. AT APRX 100' AGL,THE ACFT PITCHED UP & ROLLED LEFT, THEN ENTERED A STEEP DSCNT & CRASHED APRX 500' LEFT OF THE RWY. EXCEPT FOR THE BD, NOPREIMPACT MECH PRBLM WAS FND. THE BD WAS FND SEPD FM THE FUSELAGE WITH THE EXTERNAL LEVER (EXT LVR) SEATED & LOCKED, BUTTHE INTERNAL LEVER (INT LVR) WAS DISPLACED TWD THE OPEN PSN & THE PROTECTIVE COVER (CVR) FOR THE INT LVR WAS FND INSIDE THE ACFT. ALSO, THE INT LVR LOCK KNOB WAS MISSING 2 OF 4 LOCKING EARS. NORMALLY, THE BD IS TO BE OPENED & CLOSED BY USING THE EXT LVR & THE INT LVR IS INTENDED TO BE ACTUATED ONLY WHEN THE BD IS USED AS AN AUX (EMERGENCY) EXIT. HOWEVER,WITH THE CVR OFF, THE INT LVR WAS VULNERABLE TO POSSIBLE MOVEMENT BY UNWARRANTED PAX ACTIVITY, INTERFERENCE WITH REAR SHOULDER HARNESS, OR INADVERTENT CONTACT WITH BAGGAGE OR RECLINING REAR SEAT. THE FLT MANUAL DOES NOT ADDRESS THE POSSIBILITY OF THE BD COMING OPEN IN FLT. ALSO, THE INT LVR IS NOT LISTED AS AN ITEM ON THE PREFLT CHECKLIST.