Abductions

Prime Minister Koizumi is in North Korea today, attending a summit with tetchy neighbors.
The hot topic at the summit–abductions. Japan claims that North Korea abducted a dozen or so Japanese citizens in the 1970s and 80s. NK has sometimes completely denied this; at other times they have launched “missing person” searches in cooperation with the Japanese Red Cross.
What isn’t said is why NK would want to abduct Japanese citizens in the first place? Did these people have specialised knowledge NK needed? Was it just to cause terror and piss off Japan? Digging around on the ‘Net as not brought the answers to the surface.