I have long wondered whether the "solution" is in "double threats." The kidnapper might take A and B, and then contact the parent or owner and say "transfer $X to me in the following manner, and then (or before then) I will return A to you; if I am not followed and see that I am safe for Y days, I will then return B to you." This kidnapper is no less credible than the conventional one, because B is otherwise useless to him, and there is the fact that his "reputation" and ability to repeat the crime depends on his freeing B as promised. And the taking, and serial returning, of A and B raises the chance that payment will be made on A. The comparison is to the conventional kidnapper who says "pay me and I will return A, and if you arrest me when I take payment, my confederates will then kidnap or murder B." This is made much more plausible by the possession of B.
Imagine my surprise, or strange sense of intellectual delight, when I read recently of the theft of four well-known painings in Zurich from the E.G. Buehrle Collection. Well-known art is difficult to sell, and the criminal's intent may be to ransom the paintings. Again, how should the criminals arrange to receive payment without being found? Sure enough, although the owners have been silent and said nothing about ransom demands or payments, two or even three of the paintings, but not the most valuable, were soon "found" in an unlocked (!) vehicle within half a kilometer of the vicitimized museum. The newspapers at first reported that the art must have been too big to be carried away undetected. But the more likely story is that the "kidnappers" took A and B, so to speak, and have now returned A. They may or may not return B once they feel that the museum has kept its bargain.
The bad news is that other criminals will learn from this. A hard question is whether this "game" is a stable one. The criminals, or at least a good number of them in the future, must return B, or future victims will not be more likely to pay (and not lead the police to the criminal) to gain the return of A. And yet each criminal has very little incentive to return B. Nor are victims very good at colluding. We might imagine a state making it illegal to pay ransoms, but such a law would be very hard to enforce and it has been tried or thought about very rarely. Still, if the "double threat" crime succeeds, states may need to rethink their tools of combat.
