As I said in my opening, race, ethnicity, culture, or religion. I would agree that race alone is not the best choice. If you flip a coin over and over and get the same result time and again, it's time to consider looking to see if the coin is rigged somehow. If bombers were totally random, as the flip of a coin should be, then we would have no directive other than to suspect everyone. This however is not the case. If we continually get the same result, as with the rigged coin, it's then time to investigate further. It may seem politically incorrect, but it's our only choice. This is partly why I support the use of the infrared devices that can see through clothes, as it lessens the need for "profiling".
If one is of a certain race, it may not mean anything....it probably doesn't. If however they also belong to a certain country, it begins to mean a little more. Now add in a certain religion and culture, and now we may have something. This method is not random but does make use of the reasonable and probable grounds method better than any other method I am aware of.