So, here we go again:
1) The Ukrainian army is equipped with 9К317 Buk's.
2) The Ukrainian separatists have it too. Proof from 26th of June:
http://rusvesna.su/news/1404041521 (use Google translate).
So they both could do that. The only thing I don't understand is why some clowns here try to find any relation with Russia.