That's really blaming the wrong people. No, the screeners didn't catch them but you have to consider the volume they dealt with. I'll bet their criteria didn't allow the time, detail, intrusiveness or authority to do much , if any, better. The breakdown was months prior including ignoring the direct warnings about Bin Laden from the previous administration and ignoring some suspicious behavior they were alerted to. In fairness, I suspect those agencies also had a deluge of things they were alerted to.