THE GLIDER WAS SOARING WITH 2 OTR GLIDERS AT 4000 FT. THE OTR PLTS SAID THE ACDNT PLT RADIOED HE HAD A CTL PRBLM JUST BFR THE GLIDER ENTERED A SLOW ROTATING LEFT SPIRAL THAT CONTD TO GND IMPACT. THE PLT HAD NO PARACHUTE. THIS WAS A KIT BUILT GLIDER THAT USED A V-TAIL RUDDERVATOR FOR PITCH & YAW CTL. POST-ACDNT EXAM SHOWED THAT A CTL CABLE BTN THE MIXING BELL CRANK & THE CTL STICK FLOATING BEAM ON THE LEFT SIDE HAD PULLED OUT OF ITS CLEVIS FORK SHANK. THIS PRECLUDED PITCH OR YAW CTL OF THE GLIDER BY THE PLT. DETAILED EXAM OF THE LEFT & RGT SIDE CABLES & FITTINGS BTN THE MIXING BELL CRANK & THE FLOATING BEAM REVEALED THAT THE MIXING BELL CRANK CLEVIS FORK FITTINGS HAD BEEN PROPERLY SWAGED WITH A KEARNEY TYPE SWAGING TOOL. EVIDENCE SHOWED THE FLOATING BEAM END CLEVIS FORK FITTINGS HAD BEEN IMPROPERLY SWAGED WITH A NECOPRESS TYPE TOOL. DETAILED REVIEW OF MAINT RECORDS DISCLOSED NO RECORD THAT THE CABLES HAD BEEN CHGD OR MDFYD SINCE ORIGINAL INSTLN. CABLES (WITH TERMINAL FITTINGS ALREADY SWAGED ON) HAD BEEN SUPPLIED TO THE GLIDER BUILDER IN KIT FORM.