Roland B. Redfield was convicted of obtaining marijuana without paying a transfer tax in violation of 26 U.S.C. § 4744(a) (1) while he was an inmate at Lorton Reformatory. The district court allowed a warden to testify that when Redfield was questioned at a prison disciplinary hearing he admitted ownership of the marijuana. In this appeal we do not pass upon the disciplinary board’s use of Redfield’s admission. Our inquiry is limited to the admissibility of the incriminating statement in Redfield’s criminal trial. Before he was questioned, Redfield was not cautioned of his right to be silent and his right to counsel, as prescribed by Miranda v. Arizona, 384 U.S. 436, 86 S.Ct. 1602, 16 L.Ed.2d 694 (1966). Mathis v. United States, 391 U.S. 1, 88 S.Ct 1503, 20 L.Ed.2d 381 (1968), decided after Redfield’s trial, applied Miranda to the questioning of a person in prison for a crime that was not connected with the tax delinquencies under investigation. The role of Redfield’s interrogator did not differ significantly from that of the internal revenue agent in Mathis. In both instances the immediate objective of the officials was not to obtain evidence for use in criminal trials. Only later did the government decide to use the defendant’s self-incriminatory answers in prosecutions under the revenue laws. For these reasons we believe Mathis requires the exclusion of Redfield’s admission. Red-field’s other contentions are without merit.

The judgment is vacated, and the case is remanded for a new trial.