I believe that the "Ukranian Rebel Terrorists" are actually regular serving Russian soldiers. The Russian military did this whether they want to admit it or not.
The leader of the rebels in that area, who was an FSB Colonel until last year was boasting on the internet about downing a Ukranian Antonov right after this happened.
This is what I think the story is:
Russian military personnel operating medium range SAM system under the flag of separatist rebels thought they where shooting at a Ukranian transport. But, because of the incompetence and greed of Malaysia Airlines, MH17 was flying at a much lower altitude and probably did mimic known Ukranian flight parameters. The result, an utterly senseless and avoidable tragedy.
But who do you blame?
I would say the Russian Military. Because they did not have to pull the trigger.