Arizona U.S. Attorney Paul Charlton was fired at least in part because he wanted to establish a policy requiring the FBI to record confessions to use in Court. Charlot complained that because the FBI had a policy of not recording confessions that he had lost convictions or had been forced to plea bargain an otherwise strong case down. So why doesn't the FBI want to record confessions?
Glenn Greenwald points out that the only reason for not recording confessions has to be that the FBI does not want the jury to know what the normal procedures they use for interrogating suspect looks like.
He makes a good case. Go read his excellent post.