If they tracked him then how he did that? I think it's obvious that execution of this terrorist act would be impossible without their permission. They tracked him to get an evidence rather than prevent this from happening.
When they first identified him and his brother as potential targets of interest (years ago) they ended up dismissing them as low risk or no risk. Shit can change though, which is obviously what happened in this case.
Let's change the question a bit - what motive does the CIA have to "authorize" terrorist attacks on the US? Why would they wan to promote terrorism at home?