In April 1943 , the Polish government-in-exile led by Sikorski insisted on bringing the matter to the negotiation table with the Soviets and on opening an investigation by the International Red Cross . Stalin , in response , accused the Polish government of collaborating with Nazi Germany and broke off diplomatic relations with it . The Soviet Union also started a campaign to get the Western Allies to recognize the pro-Soviet government-in-exile of the Union of Polish Patriots led by Wanda Wasilewska . Sikorski died in the 1943 Gibraltar B-24 crash — an event convenient for the Allied leaders
1943 Gibraltar B-24 crash
1943 Gibraltar B-24 crash
Katyn massacre