In 1943 a British Court of Inquiry investigated the crash of Sikorski 's Liberator II AL523 , but was unable to determine the probable cause , finding only that it was an accident and the " aircraft became uncontrollable for reasons which cannot be established " . A popular theory was insufficient technical maintenance leading to jamming aircraft controls . Despite this finding , the political context of the event , coupled with a variety of curious circumstances , immediately gave rise to speculation that Sikorski 's death had been no accident , and may in fact have been the direct result of a Soviet , British or even Polish conspiracy .