The "Ukrainian separatists" (i.e. Russian, Cossack, Chechen soldiers and former soldiers) are likely the culprits.
1. All airliners have transponders
2. Both the Ukrainian and the Russian armies receive real-time data from Eurocontrol
3. Pro-Russian "separatists" are not linked to Eurocontrol
4. The flight had already traversed most of Ukraine without issues (going from Amsterdam to KL)
To use such a launcher requires a considerable degree of training. No amateur is going to be able to figure out how to use this:
Then there is all the circumstantial evidence of the rebels celebrating a plane shootdown around the same time as MH17 lost contact claiming they had shot down a Ukrainian cargo plane. Then hastily deleting those social media posts as they realized it was a civilian jetliner.