Prosecutors are investigating how two jailed mobster brothers managed to make their wives pregnant despite strict regulations forbidding conjugal visits.

Italian news agencies reported Friday that investigators suspect that the two men used couriers to smuggle out their sperm.

Filippo and Giuseppe Graviano have been in prison since 1994. They are accused of various crimes, including having helped carry out Mafia bombings in Florence and Rome in 1993 and ordering the killing of a Palermo priest.

Investigators realized the two men had fathered children when their wives came to visit toting babies born last year. The births of the two boys were registered and the brothers were listed as the fathers.

Mafia bosses are denied by law some privileges granted other prisoners, such as conjugal visits.

Prosecutors have complained for years that mobsters controlled their clans from behind bars by giving out orders through visitors, including wives, and managing to live comfortably in their cells with cozy furnishings and home-cooked meals.