Maybe one day we'll know which, but Russia claims that an aircraft crashed/was shot down with soon-to-be-released Ukrainean POWs (and that another similar plane turned round, in response), whilst Ukraine may or may not have shot down a plane transporting missile supplies for the conflict.
I mean, my natural inclination is to disbelieve the Russian account (but lets see how long until fuller evidence/'evidence' of the tragedy's crash-site takes to emerge), even while admitting the possibility of Ukraine making an error. Or both could be true (POW transportation on a supply plane!).
Can't see this being disentangled, easily. If the Russians want bodies in the wreckage, they can arrange it. If the Russians taunted Ukraine with 'leaked information' about this being a resupply plane and then packed it with 'POW's and their least-considered aircrew, I also wouldn't be surprised, or consider this an overly paranoid thought process (on my part or theirs). Not the first time that non-combatant aircraft have been knocked out of these skies, either, by error or otherwise.
Either way, a scheduled prisoner-exchange is now delayed (to the benefit of nobody on the ground) and the fate of particular individuals is muddied (perhaps to the benefit of others). I'll let Ukraine do its own hand-wringing over this, based upon what they actually know they reasonably knew, but I'm sure the top-tier in Russia isn't too bothered (gives them a story to spin, real or otherwise, at least to the home crowd).
And further details have probably emerged even as I write this, so can't be sure even if this post is currently accurate, nor any of my wide-ranging assumptions.