Norway has defined Breivik’s Oslo killing spree as a terrorist crime and Paris public prosecutors are responsible for investigating terror crimes in the whole of France.
Jens Breivik is retired and lives in Cournanel in the southern Aude department.
Although he has not seen his son for several years and has not lived with him since he the boy was one year old, Norwegian police believe that his testimony is important in establishing a psychological profile of the mass murderer.
But he has so far refused to return to Norway or go to its embassy in France, so the Paris officials must now seek an interview with him and invite Norwegian observers.
Anders Behring Brevik, who has admitted to the killing spree while claiming he was fighting off a “Muslim invasion” and its left-wing agents, was put under psychiatric observation to establish his mental competence on 10 February.