The exact terms by which Libya gained Aouzou remain partly obscure, and are debated. The existence of a secret agreement between Tombalbaye and Gaddafi was revealed only in 1988, when the Libyan President exhibited an alleged copy of a letter in which Tombalbaye recognizes Libyan claims. Against this, scholars like Bernard Lanne have argued that there never was any sort of formal agreement, and that Tombalbaye had found it expedient not to mention the occupation of a part of his country. Libya was unable to exhibit the original copy of the agreement when the case of the Aouzou Strip was brought before the International Court of Justice (ICJ) in 1993.