Book-lovers around the world have been helping investigators trace thousands of rare volumes looted from one of Italy's oldest libraries by a gang of thieves including the librarian himself. While most have been recovered, a number of invaluable 15th and 16th Century books are still missing.

Inside a 16th Century church complex in the heart of Naples, the Biblioteca Girolamini's wooden shelves rise up and up towards richly decorated walls and vaulted ceilings.

They once held works of extraordinary value. There was a 1518 edition of Thomas More's brilliant and mysterious Utopia. Galileo's 1610 treatise Sidereus Nuncius, containing more than 70 drawings of the moon and the stars. And Johannes Kepler's study of the motions of Mars, Astronomia Nova, described as one of greatest books in the history of astronomy.

But this magnificent piece of Italy's cultural heritage was methodically plundered. Thousands of antique texts disappeared....