"a lasting controversy over the circumstances" . "controversies and theories" . . "something of a mystery" . . . . . . "controversy surrounding Sikorski's death" . . . . . . . "W\u0142adys\u0142aw Sikorski's death controversy" . . . "Sikorski's death" . . "W\u0142adys\u0142aw Sikorski" . "controversial" . "Airplane accident" . "W\u0142adys\u0142aw Sikorski's death controversy" . . "suspicious death" .