I personally believe this act was Russia's doing - directly, or semi-directly, through their planted "separatists", but I also think it may have been an accident, in that they may have believed they were firing at a military vehicle (which is still NOT justifiable, but...).
Regardless, before we start WWIII over this, realize the US has done similar shit in the past, and like Putin, our "leader" refused to apologize as well...
https://scontent-a-lga.xx.fbcdn.net/...64&oe=544F6194