Freakonomics author Stephen Dubner explains in his New York Times blog why the "Swedish blood libel" - the accusation that Israel was deliberately killing Palestinians in order to harvest their organs - is physically and logistically unlikely:
Al Roth, the Harvard economist whose work on matched-pair organ donations has started to transform the organ-transplantation scenario, told me he found the accusation unbelievable because of the logistics of organ harvesting itself. “Organs don’t last very long and have to be matched rather particularly,” he said, “so it would be hard to take them on spec for an international market. So I think black market organs must mostly be from live donors. Live donors can take blood tests well in advance and travel to where the patient is. Deceased organs have to be put on ice, and the clock starts ticking immediately and fast.”
Another question: If you did kidnap someone in order to harvest their organs, would you really return the body to the family afterwards? Wouldn't that be incredibly stupid?