No one detected it because it emits almost no radiation- it's depleted uranium, the stuff we made artillery shells out of to harden them, relatively harmless stuff; that's why they didn't need to shield it much. Let's see the media try to slip by something that actually emits a serious signature. Then you will know if someone's paying attention. But slipping an container by labeled 'nuke' isn't a great feat if it doesn't the level of radiation that a weapon would. They may as well have painted an empty crate with the words 'big fat nuclear bomb.' It isn't a bomb, isn't big enough to be a bomb, isn't heavy enough to be a bomb, doesn't set of radiation detectors like a bomb, so why should it be detected? That's like this media company claimed that trucks were dangerous because when hit in the side the gas tanks would explode... the problem wasn't the trucks, it was that the media had rigged explosive devises on the truck to 'enhance' the 'test.' IOW, it was a bogus test done purely for publicity.
There's no way to search every crate in every shipping container in every ship, boat, plane and small craft without many, many more bureaucrats than we have. We need better interdiction capabilities, but there comes a point that if we spend all of our resources trying to prevent one type of attack, we will miss catching a plot to do another type of attack. We can be vulnerable to some suprisingly low-tech attacks, if they are used judiciously to manipulate us and divide us politically. The terrorists can have a greater impact on your economy than their numbers would suggest- their options to attack us are infinite because they are setting the terms, while our resources are limited because we don't know what they are going to do and can only guess. They don't need popular opinion to be on their side, they only need to turn popular opinion against us, against the government, and one way to achieve this is to keep the government on defense all of the time.
That's why our best solution is to pursue these terrorists and their supporters in every country, ruthlessly. We need to go on the offense. The more of them we kill, the more of their safe havens we eliminate and the more assets of theirs we destroy... the more we can limit their options by making them wonder what WE are going to do. We want them to respond to us, not the other way around. Hence the need for preemption on our part.
I cannot argue about the viability of the test, as far as radiation amounts, and their comparability to smuggling enriched uranium and getting it by current customs inspectors.
My point, and I believe part of their point, was that weapons grade material may have been smuggled over the past 4 years using that route and technique. We weren't checking for it then like we are now.
This stuff could all be in place and the past year has been spent incorporating it into real bombs or dirty bombs.
I.E. Current techniques and equipment, used by customs agents, USCG, etc. are great, but it is unlikely they are trying to get stuff into the country now. It is probably already here.