But the terrorists have proved willing to take months or even years to plan an attack.

So a terrorist could easily be someone who has passed a background check and is wearing a blue uniform with a shiny badge. Because he will have passed a background check to get his job, he will be permanently above suspicion until he does something really really egregious - and then only if video of the incident makes it to youtube and the evening news.

If a pax observes the terrorist doing something suspicious and reports it, the entire organization will rally behind him and attack the pax's credibility, media bias, etc.

Unlike federal positions where security is really taking seriously, after his initial background check, he will not be subject to routine new checks.