The recent bombings in London have got me thinking: why do terrorists always wait for a while before claiming responsibility?
One possibility is that the groups claiming responsibility may not actually have done it. Consider this: there are several independent terrorist organizations. One of them bombs London, but doesn't want to be hunted down so they don't claim responsibility. Al Qaeda (actually their European division of Abu Hafs al Masri Brigade) is already in trouble with the free world, so they claim responsibility instead. Maybe there's some understood "grace period" among terrorist groups after which anyone can claim it. Really, how much more trouble could Al Qaeda get in? It makes sense they would take a fall, allowing a different terrorist group to remain unknown.
Or, it could just be incompetence. Maybe they're afraid of failure enough that they have to wait until the act of terrorism is complete before claiming responsibility. And if they're going to wait that long, they may as well put it off for a while longer, because there is a psychological edge to not knowing who your enemies are. Remember: the objective of terrorism is not killing people; it's causing terror. Purely psychological. Long term goals - e.g., controlling the foreign policy of another country - require a state of continuous terror for a large portion of the population, which is difficult to achieve. Terrorism attacks have to maximize the effect on the psyche, not maximize the damage done.
Still, I don't think waiting so long to claim responsibility is a good idea. There's a better way to achieve the objective of terror.
Let's assume I run a terrorist organization, and I wanted to cause terror in a particular country. I would not have a surprise bomb go off, and then let everyone wonder who was responsible for a few days before I announced "um, yeah, that was me... wait, let me check... ok, yup, it was me."
I would announce it ahead of time.
Not the specifics, of course. First, specifics would just help the police catch me. Secondly, the terror is increased if people are aware of impending danger but don't know where it is. For example, it would be bad to say that I will bomb a New York subway next week - too specific. I would say instead that I will set off a bomb in New York one week from that announcement. Let the populace of New York wonder where the bomb will be.
Of course, there are additional dangers when announcing terrorist attacks ahead of time. The entire city will be alert for danger on that day. However, it is just not feasable to be able to defend against such a general announcement. What are they going to do - shut down New York for a day? Even with all civil servants, including militias and other civilians, it would still not be possible to secure such a large target. This is due to a fundamental principle of security: it is much harder to defend than to attack. For good discussions of this principle, I refer you to Bruce Schneier of Counterpane Internet Security. He's liberal in his political views, but he understands security better than most people.
However, even though it is not possible (well, ok, not feasable) to secure a large city, there is still a greater chance of failure compared to a normal surprise terrorist operation (since they know it's coming). And that is something I could not allow. I would want my organization to become well-known in the psyche of the victim country; and the best way to do that is simple: keep my word. If I say a bomb will go off in a given city on such-and-such a date, it better happen. Or else next time people won't be terrorized. Even one failure would cause huge damage to the terror potential; it would be better to do it the way the current terrorists do rather than to fail even one time trying it this way. So, I would need to take extra precautions against failure.
The general idea would be to announce one bomb going off, and then dispatch about a half-dozen independent teams into the city on that day. "Independent" meaning that they have no contact with each other, or even have any idea how many other teams are in the city. Each team would be given a specific target and a unique time for detonation. However, I would only want one bomb to go off in that city. That way, no-one can ever be sure how many teams I had in there. So, if one team sets off their bomb, none of the other teams will. This requires some form of communication, which is not allowed since each team must be completely independent. So, they would also be given a small, portable TV. Any bomb going off in a large city will hit local news within two hours (more like ten minutes, but say a couple hours to be on the safe side). The procedure is simple: proceed to your target and watch TV. If you see a bomb on the news, return to base; otherwise, if your target time arrives and there is no bomb on the news, assume all previous teams have been captured and detonate yours. Simple.
Well, that's how I would organize attacks if I was a terrorist.
One final note: remember, the objective is to strike terror. Currently, it seems the terrorists only attack the day-to-day businessmen. Planes into office buildings; bombs on subway trains. If all you ever attack is subways, then that makes the defense a lot easier. I would branch out to a lot of other targets, while also keeping the classic subway/office building/restaraunt repertoire. I'm talking schools, supermarkets, day cares, nursing homes, churches, rock concerts and playgrounds. If you're going to play dirty, play dirty.