I am from the Netherlands, where most of the casualties are from: can we PLEASE stop our uninformed finger pointing until at least some evidence turns up?
None of us know what happened.
Russia or the separatists in Eastern Ukraine might have done this -- although no-one is sure what they would stand to gain from it. Ukraine's own military might have done it (they've done it before and denied it vehemently until it was proven beyond a shadow of a doubt).
When did they do this before? If they had, we would have definitely heard about it because YOUR dictator Putin would never shut up about it if it did. Fuck off, Russian troll!