I would tend to agree with you Keith that there is little doubt as to what happened, especially considering the intercepted radio exchanges between "Separatists" and "Russian" Security Forces shortly after the aircraft was shot down. The culprits would most probably be "Separatists" operating a missile system smuggled to them by the Russians or looted from a Ukranian Army base (As the "Separatists" do not have aircraft there is no reason for the Ukranian Armed Forces to have such systems deployed in the area - there being no air threat).

Trouble is these missiles are normally part of a larger integrated air defence system with quite complex and comprehensive command and control networks. Deployed in isolation and being operated in "local" control it becomes very difficult to positively identify your target before firing.

The aircraft should have been safe at its normal cruising altitude and its route was considered safe as the flight plan must have been filed and approved.