I don’t believe the CIA let it happen. I surmise that they, like you Arraya, didn’t want to give credence to the idea that he, as a muslim, could be more susceptible to jihadist philosophy than a christian and they did not analyze or care to understand how the core teachings of Islam can lead one to jihadism.
That’s how I feel.
There is evidence for my hypothesis. There is zero evidence for yours. When this situation happens, the one with zero is the whack job.