This could only be done with Russian equipment.
It was apparently shot down by a Buk SAM system. Both the Ukraine and the Russians have these, not sure about the separatists, but it’s certainly plausible.
The plane was traveling west-to-east, so I doubt the Russian army would mistake it for a military transport, their radar had plenty of time to pick it up and ID it. That leaves the separatists and the Ukranians as possible perps.
http://en.wikipedia.org/wiki/Buk_missile_system