We may never know the truth about what happened.
Would Russia invade Turkish air space? Without hesitation.
Yet, Turkey's response to ISIS has been less than admirable. For many months they refused to allow the Peshmurga (of the Turkish Kurds) to cross the Syrian border to engage ISIS at Kobani, where many Kurds were being slaughtered by the terrorists. It's clear that Turkey would rather face the threat of ISIS (who they hope will stay in Syria and Iraq) rather than allow the Peshmurga to gain extensive combat training which they might, at some future time, use to re-establish Kurdistan.
So Turkey, in shooting down a Russian aircraft, assisted ISIS. But was that their motive or were they really only preserving national air space? And was the decision made by the pilot, or his commander on the ground, or at a government level?
There'll be lots of interest in this over the next few days.