Re: Does it really matter who shot it down?
1) This was an attempt to assassinate the leader of the world no.2 nuke weapon power...
2) ... the intention was to deliberately bring down any passing commercial transport, intending to implicate the other side (a false flag attack).
There is perhaps a third option, the "Vincennes excuse", in which those who launched the missile intended to bring the plane down, but in the red mist they'd ignored the obvious signs that this was a non-combatant
I would rate the probabilities as 90% option 3 (screw up), 9.9% option 2 (false flag) and about 0.1% option 1 (shootin' Putin)
There is a possibility of a mixed option 3 and 2 - when the missile was fired by the separatists but based on "injected intelligence" - I would quantify it as 20%-30% (within the above 90%).
I say this because it is easy to hit a wrong target by mistake when operating a SAM like Buk.
The crew tracking a target sees primarily the bearing, range and elevation data on 2 or 3 separate indicators. They don't see the altitude directly. There normally is an optical tracker with a nice telephoto lens and IR capability but it's use in an engagement is optional, it is visible to only one crew member, its probably BW and if there is a cloud cover there is not much use in it anyway.
They also have an IFF interrogator but I'm not sure that it would have picked-up a civilian transponder response and the normal SOP will be for the crew to use it manually a couple of times before launching the missile. I am pretty confident that the separatists crew (if it was them) would have ignored the IFF because they would have expected any target to be hostile (they had no "friendly" A/C) and without agreed codes the IFF is useless anyway.
So, a mistake would have been easy to make - but precisely because of that they should have taken a lot of extra care and they clearly hadn't.