Russians have never had any problem with killing people, even its own, which by modern accounts historian Norman Davies puts Soviet deaths of their own people (i.e., the Revolution of 1917 to the fall of communism in '89) at >55 million conservatively.
IMO This is the reason responsability must be taken. In order to change the full history. Russia knows that with "Katyn" comes 1.8 million sent to Siberia, killing of Polish officers that were serving as allies, not to mention there own military if they tried to assist Poland. It's the domino effect that Russia has kept from falling. Here is some of the outcome. Many feel Poland should have just left the meeting.
"The sessions of the Polish - Russian historical commission have not gone very smoothly either. The commission gathered to explain all circumstances, as the members said, of the crime committed by Stalin's regime and finally solve the question of the Katyn genocide. However, opening the meeting, Russian foreign minister said it was a heresy to compare Stalin's rule with Hitler. Commentators started wondering what does each side consider as solving the divisive issues. Examining the truth or shutting down the debate once and for all?"
"Finally, after two days of discussions, the commission decided on a joint publication. Polish and Russian historians are to describe most controversial issues from their separate points of view and these are to be published within one book, chapter by chapter in two voices. The book is to be out in two languages in 2009."
"This Russian attempt to revise history, although not supported officially by the Kremlin or Russian authorities are aimed at a propaganda effect among Russians and many
simple Russians indeed believe it's true.'"
polskieradio.pl/zagranica/news/artykul94680_Polish_Russian_