A federal judge on Thursday didn't allow the airing of the audio, some of which was made after the agents wondered aloud whether they were being recorded. At least one recorder was indeed still running.
An undercover agent identified only as "Hussein" was posing as a radical Islamic jihadi during the FBI investigation into Mohamed Mohamud of suburban Portland.
"Hussein" confirmed under cross examination Thursday that he said it was "fantastic" after Mohamud asked for explosives, a crucial step in the sting operation that culminated with Mohamud's arrest in November 2010.
Mohamud has been charged with attempting to blow up Portland's 2010 Christmas tree-lighting ceremony. The bomb was a fake provided by the FBI.