The deliveries came to light after authorities at the prison, located some 444 km (275 miles) from Sao Paulo, noticed a growth in drugs and mobile phones seized from prisoners.
A subsequent crackdown, as well as the installation of a new security system, failed to reveal the source of the forbidden goods. However, the strange behavior of pigeons on the roof of the jail attracted the attention of the guards.
Prison officers later found out that some of the birds had special containers attached to them. According to the jail authorities, one of the prisoners had managed to tame the birds and make a nest in his cell, and the pigeons were then passed on to friends outside the prison with visitors. The birds later returned to the prison carrying their valuable 'cargo.'