The accident happened over Ukraine territory, as a result, the Ukraine is responsible for the safety of all its overflying traffic.
It's remarkably nonsensical to suggest that just because this happened over Ukranian airspace the Ukranians are responsible for it. That's like saying Sept 11th happened in US airspace and so the US are responsible for it. Wrong! The people who decided to pull the trigger are responsible for this, and - whoever they happen to be - should be brought to justice.