I read a very interesting theory about this airstrike a few weeks back. Here it is in a nutshell. Syria, according to this article, possesses the most crowded anti aircraft system in the world following its continued purchase of Russian weapon systems. Dayr az-Zawr, where the F15/16 attack took place, is not just a tip toe across the Syrian border. The Israelis would have had to fly deep into Syria to get there. And what happened with Syria’s super dooper anti aircraft system? Nothing. No evidence of enemy aircraft in Syrian airspace. The Israelis, with a little technical assistance from their good ole friends in the USA, were able to totally blind the Russian anti-aircraft system. Hence, the silence on the part of Syria when this happened. They thought they were totally protected and ended up naked. Also, this served as a warning to Iran as to what we’re capable of doing. Just a theory….. an interesting one.
Today this is the story:

The September Israeli airstrike on a suspected nuclear site in Syria had been in the works for months, ABC News has learned, and was delayed only at the strong urging of the United States.

In early July the Israelis presented the United States with satellite imagery that they said showed a nuclear facility in Syria. They had additional evidence that they said showed that some of the technology was supplied by North Korea.

Read more at ABCNews