Below is a link to an interesting article in the Modern Tokyo Times that describes a possible approach to use for prosecuting family members and others who may be engaged in assisting child abductors.

Under the Pinkerton Rule, “each member of a conspiracy can be held criminally liable for the crimes that were committed by other members acting within agreement of the conspiracy”:

http://moderntokyotimes.com/2011/07/18/japan-time-for-america-to-extradite-the-relatives-of-parent-abductors/