According to this ABC News report, the US requested, and got, a delay in the attack because they were concerned about the accuracy of the Israeli intelligence showing an ambitious nuclear facility, and possible repercussions.

I may have been wrong in my previous assessment that it was not a nuclear facility, but as the sources could for the ABC story could be political appointees, I still lean against it being a nuclear facility.

Simply put, Syria does not have the infrastructure to even begin any sort of nuclear weapons development.

As to the sourcing, it could be some mid-level intelligence professionals, or some politically appointed yahoo like John Bolton.