Do you have a link to any evidence, or just conjecture?
To date the facts are that it was a Russian manufactured launcher in eastern Ukraine. All involved parties possess and are trained to use such launchers. All involved parties are putting out conflicting stories. It is an active war zone and propaganda is to be expected. The missile was fired it by unknown person(s). No definitive proof exists to say otherwise. NATO has not made a statement saying that evidence exists to show who did it.
Just wait a few days — the Malaysians are going to release their preliminary report on what is known thus far from the facts on the ground and those little Orange Boxes and other viable sources.