don't have a cat in this fight or whatever it is but what exactly Putin gains by having the Polish President killed
Probably constant quarrels on Polish political scene between the ruling camp (PO + PSL) and the party (PiS) of that deceased President.
And, by the way, not only the President was killed but also - for example - the bulk of Polish Armed Forces Leadership, including these men:
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Gen. Franciszek Gągor, Chief of General Staff of the Armed Forces of the Republic of Poland
Lt. Gen. Tadeusz Buk, Commander in Chief of the Land Forces of the Republic of Poland
Gen. Andrzej Blasik, Commander in Chief of the Air Forces of the Republic of Poland
Fleet Admin. Andrzej Karweta, Commander in Chief of the Polish Navy
Lt. Gen. Włodzimierz Potasiński, Commander in Chief of the Special Forces of the Republic of Poland
Gen. Bronisław Kwiatkowski, Operational Commander of the Armed Forces of the Republic of Poland
Maj. Gen. Kazimierz Gilarski, Commander of the Warsaw Garrison
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And more:
http://smolenskcrash.eu/smolensk-victims