The commission concluded that the bodies of some of the passengers showed signs of damage that could not be explained by fires which broke out at the crash site in western Russia, Radio Poland reported.
The commission also said that the Russians opened the presidential plane's black box without Poland's knowledge and that five seconds of recording were cut from a Russian flight recorder.
Read alsoPutin-Tusk recording contradicts Polish and Russian reports - MacierewiczThe commission also said that some remains of the plane were found at least 60 meters ahead a birch tree which, according to previous reports, the plane clipped.
An earlier report said that hitting the tree was a key factor in the disaster.
The findings were presented at session of the Polish parliamentary defense committee on Friday.
The commission was set up by the governing Law and Justice (PiS) party which came to power last October.
The party is headed by Jaroslaw Kaczynski, twin brother of Polish President Lech Kaczynski, who died in the crash in Smolensk, western Russia, along with 95 others.
PiS has long challenged an official report into the crash issued by the previous Polish government which cited a catalogue of errors on the Polish side, while also pointing to errors made by Russian staff at the control tower of Smolensk Military Airport.
A Russian report placed all the blame on the Poles.
Polish Defense Minister Antoni Macierewicz said earlier this week that a video recording of a 2010 meeting between Russian leader Vladimir Putin and then Polish PM Donald Tusk hours after the crash prove that an official Polish report was a direct copy of a "falsified" Russian report on the disaster.