bjcc (and everyone else), please forgive my pedantic behaviour as I place my forehead back against the wall.
Again you said,
In any event it was an example to show that such items can be taken airside without the knowladge of the person carrying them. A member of crew wouldn't carry something they didn't know the contents of? Think again it's happened!
The first sentence is referring to some one carrying something without knowing they were doing it, such as the lady in the El Al incident. You managed to catch me out completely by tying your second sentence together with that. You see I thought we were talking about people attempting to put weapons or explosives covertly onto aeroplanes.
The examples you gave; presumably the Captain wasn't carrying either of the above (although I accept from what you say that perhaps, maybe he possibly could have been......) but he knew he was carrying something!
As for this "tear gas canister" the stewardess was carrying in her purse - the full riot control variety was it??
I think the post by ivor lobbon just above has brought us back to the burning question: why are flightcrew treated as a special target by security?