From Wikipedia:
So what if Jarrah was actually reticent and not only withdrew from the plot but attempted to turn in his compatriots, could it still have been prevented reasonably or would he have been ignored?
In mid July 2001, some of the hijackers and members of the Hamburg cell gathered near Salou, Spain, for a period of a few days up to a couple of weeks. There seemed to be tension between Jarrah and Atta about the plot in its late stages. Atta had complained to Binalshibh about his difficulty in getting through to Jarrah and his fear that Jarrah might withdraw from the plot completely.
So what if Jarrah was actually reticent and not only withdrew from the plot but attempted to turn in his compatriots, could it still have been prevented reasonably or would he have been ignored?