Apparently the president of Ukraine was on a state visit to Oman when this happened. He is cutting that short to return to Kiev. I’ve read speculation elsewhere that the plane could have collided with a surveillance drone or may have been in the line of fire when Iranians tried to shoot down a higher flying surveillance aircraft or a drone. There are important military bases in the general area of the crash site.
Personally I doubt that this was anything to do with eliminating witnesses in any potential U.S. legal cases. The passenger list will probably turn out to be mostly unfortunate regular civilians visiting relatives in Iran over the holidays (which may explain the large number of Canadians on board, there is an Iranian community in Canada, mostly people who left forty years ago, and the connection would be that Ukrainian Airlines flies to both Tehran and Canada from Kiev. Or possibly another airline for the longer flight. RIP.
To be sure, that’ll be twisted to Trump’s fault.