We already know who fired it. Russian-backed rebels in the Ukraine fired it, thinking that they had shot down a Ukrainian military jet. We know from intercepted radio transmissions that they didn't think they were shooting a civilian plane, we know they thought it was military, and they were celebrating that at first, until they started hearing that it was in fact a civilian plane. Then they started trying to cover it up.
This is one of those cases where the coverup is worse than the crime.
There isn't much of a crime here underneath all this -- some guys fucked up and shot at the wrong thing in a war zone. That happens. When Israel or the US does it you insist it's a war crime, but in fact all sides do it from time to time, and in this case, these Russian backed rebels did it. They'll have to live with that on their conscience, but it isn't a war crime to fuck up and shoot the wrong thing by mistake.
On the other hand the COVER UP is pretty interesting. Instead of fessing up and apologizing they tried to hide the evidence, tamper with the scene, interfere with investigators, and Russia itself may be complicit in that coveraup. For that heads should roll, probably all the way up to Putin, although he's a dictator, so he has no accountability whatsoever.