[glenra]

> it is unusual a person and their items could fail so many times using different testing equipment.

So maybe it's finding something true. BFD. You look in the bag, verify there's no explosive there, and let him through.

Maybe the bag had fireworks in or near it at some point. Or magician's supplies. Or a chemistry set. Or any number of other things. There are a dozens reasons why a bag might actually have been near explosives or chemicals that are similar enough to explosives or explosive precursors that the test would correctly show positive.

Nobody cares whether the test result was an error or a "correct" reading based on something that IS NO LONGER IN THE BAG - either way, you let him through. Why the hell not?

[mintplant]

Or it could be somewhere hidden in the bag, in a lining somewhere, etc. Or it could be somewhere else on his person, having left traces on the bag after coming in contact with it.

[glenra]

Right, that's why they do a search. Amd if it's hidden so well you won't find it in a search, it'll be hidden that well tomorrow too - where is the sense in pestering this guy for hours and sending him home to get on a plane tomorrow rather than letting him get on a plane today?

The sad truth is that the terrorists here are us. The primary reason nobody has blown up a plane recently in the US is that nobody is TRYING to blow up a plane in the US. If somebody were seriously trying, they'd have done it already.