Italian officials have handed to the FBI a Bible that belonged to suspected Mafia kingpin Bernardo Provenzano to see whether it contains a secret code.
Bernardo Provenzano allegedly took over the Mafia in 1993
Provenzano, 73, was captured in Sicily in April after 43 years on the run.
The Bible found in his isolated hut contained dots, arrows and notations and investigators want to know if it is a code that will unlock other messages.
Provenzano, who allegedly took over the Sicilian Mafia in 1993, is held in a top security prison in central Italy.
Italian prosecutor Piero Grasso said: "We need to do everything we can to see if Provenzano's Bible contains coded messages."
Prosecutors say Provenzano constantly refers to the book, found in the hut close to his birthplace in Corleone where he was caught.
Provenzano was arrested at an isolated hut in April
The hideout contained paper notes known as "pizzini" which had numbers that Italian code-breakers said referred to Mafia contacts.
Mr Grasso said it was still to be proved whether a code existed. If there is one it could help police prevent the Mafia from reorganising.
Mr Grasso said Italian authorities had co-operated with the FBI over the Mafia "many times".
A US government official confirmed the FBI was "working with the [Italian] state police to determine whether there are any hidden messages in the Bible".
Any code-breaking will be done at an FBI laboratory in Quantico, Virginia.
Italian police say Provenzano took over as head of the Cosa Nostra in 1993 after then leader Toto Riina was captured.
Provenzano was given the nickname "Binu the tractor" for allegedly mowing down enemies as a hit man.
While on the run, he was sentenced in absentia for murder. A package of laundry sent by his wife led to his capture in April.