The French investigation into this month's Paris shootings is exploring the possible role of Djamel Beghal, an Islamist suspected of first bringing the gunmen together and putting them on the path from impressionable youths to cold-blooded killers.
While the 49-year-old Algerian has denied through his lawyer any involvement in the attacks, judicial and prison sources have described how two of the three gunmen nonetheless fell under his spell during a joint 2005 stretch in jail and then pursued contacts with him after leaving prison.
"Beghal is the crux of the case," said a source close to the inquiry, which last week ordered searches in the cell in the high-security prison in the western city of Rennes where he is now serving time for an unrelated conviction.