As the acft was taxiing for takeoff, witnesses noted the L rear baggage door was unlocked & hanging down. A warning was relayed to the plt via the twr, but by then the acft was airborne & the plt had rprtd a control prblm. Drg lift-off, the acft pitched up sharply & entered an immediate rgt bank of abt 45 deg. As the gear retracted, the bank angle decreased to abt 20 deg. The acft was rprtd to yaw slightly fm side to side & circle to the rgt while climbing to abt 1000'. A witness (in radio ctc) asked the plt abt the problem; the plt replied the controls (ctls) were locked to one side. On advice of otrs, the plt tried to ctl the acft with eng power adjustments, but the acft lost alt to abt 200' AGL. Subsequently, while mnvrg, it struck a tree, then hit a utility pole & crashed. Drg impact the lower fuselage, which housed the flt ctl linkages, was badly dmgd. No preimpact mech prblm was verified concerning the flt ctls, autoplt or trim. A plt, who had previously flown the acft with the baggage door open, said he experienced no adverse ctl prblms.