Read Malcolm Gladwell's article, "Criminal Profiling Made Easy."

Loosely paraphrased:
According to US Customs, suspicious activity included:

- Traveling with or without baggage
- Traveling in the front, middle, or aft section of the plane
- Traveling alone or with other passengers
- Checking in early, on time, or late
- Being the first to get off the plane, the last to get off the plane, or somewhere in the middle

I actually support some forms of profiling and behavioral detection since our "one size fits all" screening methods are cumbersome, expensive, insensitive, non-specific, humiliating, over-the-top, etc.

But detecting unusual or specific behavior is not an exact science. For this reason, I don't think that detection is the issue, it's how you react.

Some examples.

Let's say that you're a US Airways Express/Chatauqua Airlines crewmember. If a passenger is acting strangely, like praying and wearing tefillin, you might find this suspicious. If you've never seen it before--yes--it's unusual. But you react by being polite, friendly, approachable, and asking "what is that? I've never seen that before." You don't divert the plane.

Let's say that you're a Continental Airlines flight attendant. A passenger pauses to look out the window of an exit door. If you're a bit paranoid, you might find this suspicious. You should react by being polite, friendly, approachable, and saying, "Hi. Are you just looking out the window? Can I get you anything... here I'll bring it to your seat." You don't scream across the cabin "Get away from the door."

In other words, these crewmembers were observing perceived unusual or suspicious behavior. There's absolutely nothing wrong with that. But their reaction was completely inappropriate.