▁taken ▁prisoner ▁in ▁ 1 9 3 9 ▁and ▁murder ed ▁by ▁the ▁S ovi ets . ▁The ▁Soviet ▁government ▁said ▁that ▁the ▁Germ ans ▁had ▁fabric ated ▁the ▁discovery . ▁The ▁other ▁Al lied ▁govern ments , ▁for ▁diplom atic ▁reasons , ▁formally ▁accepted ▁this ; ▁the ▁Polish ▁government ▁in ▁ex ile ▁refused ▁to ▁do ▁so . ▁ ▁St alin ▁then ▁sever ed ▁relations ▁with ▁the ▁Polish ▁government ▁in ▁ex ile . ▁Since ▁it ▁was ▁clear ▁that ▁it ▁would ▁be ▁the ▁Soviet ▁Union , ▁not ▁the ▁western ▁Al lies , ▁who ▁would ▁liber ate ▁Poland ▁from ▁the ▁Germ ans , ▁this ▁bre ach ▁had ▁f ateful ▁consequences ▁for ▁Poland . ▁In ▁an ▁un fortun ate ▁coinc idence , ▁S ikor ski , ▁widely ▁regarded ▁as ▁the ▁most ▁capable ▁of ▁the ▁Polish ▁ex ile ▁leaders , ▁was ▁killed ▁in ▁an ▁air ▁crash ▁at ▁Gib ral tar ▁in ▁July ▁ 1 9 4 3 . ▁He ▁was ▁succeeded ▁as ▁head ▁of ▁the ▁Polish ▁government ▁in ▁ex ile ▁by ▁Stanisław ▁M iko ł aj czy k . ▁ ▁During ▁ 1 9 4 3 ▁and ▁ 1 9 4 4 , ▁the ▁Al lied ▁leaders , ▁particularly ▁W inst on ▁Church ill , ▁tried ▁to ▁bring ▁about ▁a ▁res umption ▁of ▁tal ks ▁between ▁St alin ▁and ▁the ▁Polish ▁government ▁in ▁ex ile . ▁But ▁these ▁efforts ▁broke ▁down ▁over ▁several ▁matters . ▁One ▁was ▁the ▁K aty ń ▁mass acre ▁( and ▁others ▁at ▁Kal in in ▁and ▁Kh ark iv ). ▁Another ▁was