It has been published this morning in the Russian news that there is an internal investigation being carried on by the security service of Ukraine concerning potential unintentional launch of a BUK missile by the army on the day of tragedy.
Do not trust any press, but here is the original article:
http://ria.ru/world/20140725/1017459906.html
Just briefly explaining what is there.
It is written that after some BUK batteries arrived into the Donetsk area a few days prior to the event, a training campaign for the BUK crews was planned and implemented (as the crews were untrained). To be closer to the reality, a couple of Ukrainian Su-25 flew over from the Nikolaev and Dnepropetrovsk area to simulate the real targets that the ground crews should train with. Everything should have been "real", except for after "pressing the launch button" the missile should not be ignited and the whole BUK complex should remain in a simulation mode. A version to be investigated in detail implies that the ground crew of a particular BUK complex deployed near the village/town of Zaroschenskoye (south of Shakhtersk, close to the line between the rebels and the regulars) indeed acquired one of Su-25 as a target and the system started followed him. The ill-fated 777 was flying above Su-25 entering into the beam cone of the BUK radar. Then for unknown reasons the missile was launched (some experts say it indeed may happen if the system hardware was not duly reconfigured - AV) and since that radar cross section of 777 is much higher than that of Su-25, the missile chased the MH17. System wise, having two angular variables identical for both planes should not be enough, as there always is the third one - range. Was it because just the wrong plane was selected by the operator, or maybe the range channel did not work properly is difficult to say.
Again, could well be another piece of disinformation, but the whole situation is very similar to what happened in 2001 when the Ukrainian army was training in Crimea and hit (with S-200) the Tu-154 flying over the Black Sea coming from Israel to Siberia. Moreover, in 2001 the S-200 operators had enough time to realise that the missile was kept flying for much longer time and distance than to the target and could issue a self-destruction command (but did not do that probably being not trained/attentive enough). Here, the ground operator obviously did not have enough time to divert/destruct the missile.