The US Federal Bureau of Investigations (FBI) has failed to decrypt five hard drives protected by the open-source encryption software TrueCrypt.
Brazilian news site Globo reports that the hard drives belong to Daniel Dantas, currently under investigation by Brazilian police for money laundering.
After five months of failed attempts to access the hard drives, Brazilian authorities requested assistance from the FBI.
The FBI tried to bypass the encryption password by using a program called 'dictionary', which randomly tests multiple password combinations until the right one is found.
The FBI was reportedly unable to get past the advanced encryption system, and returned the hard drives to the Brazilian police.
Under Brazilian law, the police do not have the right to force either Dantas or TrueCrypt's makers to reveal the passwords used to protect the hard drives.
Dantas has been arrested twice by Brazilian police as part of the investigation, code-named Operation Satyagraha, into money laundering allegations, but has been released without charge on both occasions.
Dantas has, however, been arrested for attempting to bribe a police officer, and has been sentenced to 10 years in jail.