PARIS, Oct 17 (Reuters) - French police arrested a former member of Ivory Coast's military special services on Wednesday as part of an investigation into the disappearance of a journalist in Abidjan four years ago, a judicial source said. Jean-Tony Oulai, already under formal investigation for the kidnap and illegal detention of French-born Canadian journalist Guy-Andre Kieffer, was detained after leaving his lawyer's office in Paris, a police source said. His arrest was ordered after Oulai ignored a summons to answer questions by an investigating judge after a witness implicated the former soldier in the Kieffer case. Local media have long speculated that Kieffer, who reported for specialist publications on Ivory Coast's cocoa industry, had been kidnapped or murdered whilst investigating corruption.