AreOut - I think it had to be the responsibility of Kiev, especially after the AN26 was shot down.
The rebels did not target the MH flight specifically, I think they genuinely thought they were firing at a Ukrainian military transport. The reaction of Mykola Kozitsin sums it up when he learns it was a civvie. "What the **** were they flying in here for? There's a war on!"
His question was rhetorical but a very fair one.