The Hogan brothers (D) were indicted for importing marijuana after Carpenter, the pilot of an airplane owned by one of the brothers, was arrested in Mexico at a deserted airstrip. A pouch containing $15,000 was found on the plane, and 6000 pounds of marijuana was found in a truck parked near the airstrip. After his arrest, Carpenter gave statements to Mexican and U.S. officials which implicated D in the conspiracy. When he returned to the U.S., Carpenter was called to give grand jury testimony in a related case pending before the same court in which D were to be tried, but before a different judge. After refusing to testify, Carpenter was given immunity and denied that he or D were involved in a conspiracy. He also testified that the confessions he gave in Mexico were wholly fabricated and resulted from torture. He was indicted for perjury. At trial, the prosecutor announced during his opening arguments that he intended to call Carpenter, that he expected him to exculpate D, and that he intended to impeach such exculpatory testimony with the confession. D objected to Carpenter's testifying because the prosecution was calling him solely to impeach him. The testimony was admitted. D appeal their convictions.