The Codex Calixtinus, a 12th century collection of sermons and liturgical passages, vanished from a safe deposit box in the cathedral, the endpoint of the ancient pilgrimage route the Camino de Santiago.

The elaborately illustrated manuscript, considered an important part of Spain's cultural and religious heritage, has yet to be found, though the police say they are close.

The key suspect is a man who was sacked after working for the cathedral as a caretaker, electrician and odd job man for more than 25 years, police said in a statement.

Police said they had also recovered at least 1.2 million euros ($1.5 million), eight copies of the Codex and other ancient books that had also disappeared from the cathedral, during searches of garages, houses and storage rooms.