Answer: the Miranda warnings had been given
Explanation: the Supreme Court in Miranda vs Arizona held that statements of criminal suspects made while they are in custody and subject to interrogation by police may not be admitted in court unless the suspect first had certain warnings read to him beforehand; these warnings are the famous Miranda rights.
In 1968, Congress passed a law as part of the Omnibus Crime Control and Safe Streets Act of 1968. This statute directed federal trial judges to admit statements of criminal defendants if they were made voluntarily, regardless of whether he had been read his Miranda rights.
Charles Dickerson had been arrested for bank robbery as well as using a firearm during a crime of violence, both of which are federal crimes. He however moved to suppress statements he made to the FBI because he had not received the Miranda warnings before he spoke to the FBI and the district court suppressed the statements.