In 1965 French agents in Paris helped kidnap and disappear Mehdi Ben Barka, a Moroccan dissident and global left-wing activist. He was taken to a villa in Paris where it is believed he was murdered by Moroccan security officials. His body has never been found. The case became a national scandal in France. The BBC's Alex Last hears from Bachir Ben Barka, who is still fighting to find out what really happened to his father.