I think that the facts will be very clearly established over the coming days.
For a start, that region has good radar coverage.
Secondly, it's under massively scrutiny from the rest of the world. I bet the US could tell you what each Russian separatist had alone for breakfast this morning, let alone if they were acquiring and firing Soviet surface-to-air missiles.
This is what the CIA lives for. They'll know all the Russian missile signature like the back of their hands. It wouldn't surprise me if they had good enough imagery to determine which finger the firer used to press the 'launch' button.
That of course is only relevant IF a missile were involved.