Well, the likelihood that the Ukrainians shot the plane down is slim (but not non-existent); the separatists, if they captured these weapons from the Ukrainians, waited for a long time to use them; and the likelihood that these weapons came from Russia is rather high.
Do you have any specific terrorist events when as much was understood going in?
Just small stuff, the Time Square bomber, the Boston Marathon bombers. It didn't take them long to get all the facts, but once known they hemmed and hawed over the Islamic ties.
-PJ