Russian invasion of Ukraine

The US knows exactly what happened as they have local AWACS at all times.

From my understanding, not exactly.

If your question is who fired it and where did it come from, AWACS usually does not provide sensor coverage all of the way to the ground. They don't see everything all the time from ground to sky. Or at least that is what I was told when I asked a friend who works in that area. Depends on weather, range, sensors operating, terrain, distances etc etc

Edit: he did also say that AWACS is great at missle tracking if fired from and over a calm sea or pancake flat terrain with few trees or buildings.