An engineer from the University of Akron, Wieslaw Bienieda, did simulations which suggest that crash could not have happened the way it was described by the Russians (http://www.cleveland.com/science/index.ssf/2012/04/university_of_akron_engineerin.html). He reported that a large debris field and no crater would be unlikely if the plane clipped a birch tree 30-40 meters (100-130 feet) in the air. In addition, he thought that many of the passengers in the midsection would have survived a fall into soft soil.
A Danish scientist, Glenn Joregensen, also was left with several questions which were not explained by the official report (http://www.smolenskcrashnews.com/6-questions-for-maciej-lasek-and-the-authors-of-the-official-polish-smolensk-crash-report.html).
I have no way of knowing what the truth is. The Dutch investigation of the MH-17 crash showed how detailed an investigation could be, and led Poles to ask if the Smolensk crash should be further investigated (http://www.smolenskcrashnews.com/Smolensk-Crash-Investigation-Requires-Correction.html). So, I do think that returning the plane to Poland where it can be subjected to a full investigation is appropriate. It's time to clear the air. Unless there is something to hide.