Whether the Court of Appeals had authority to issue habeas corpus while McCann's direct criminal appeal was pending.
Holding
Yes. The Court of Appeals had authority to issue the writ as an auxiliary measure in aid of its existing appellate jurisdiction, and it did not abuse that authority in these exceptional circumstances.
Reasoning
Federal courts have long possessed statutory authority to issue auxiliary writs necessary to the exercise of their jurisdiction. Under Whitney v. Dick, a court of appeals may not use habeas corpus as an original, independent attack on a judgment from another court when no appellate proceeding is pending. But McCann had already appealed his conviction, so the Court of Appeals had existing jurisdiction to which the writ could be auxiliary.
Habeas corpus ordinarily cannot substitute for a direct appeal. Yet the Court rejected a narrow view that a writ is available only when appellate duties literally could not otherwise be performed. Unless Congress has restricted the remedy, an appellate court may use historic auxiliary writs when, in its sound judgment, they reasonably aid the fair and effective exercise of its jurisdiction.
The Court of Appeals reasonably found exceptional circumstances here. McCann was indigent, remained in custody because he could not make bail, lacked access and opportunity to prepare a bill of exceptions, and faced a real risk that his full appeal could not be effectively heard. The writ addressed a discrete question without forcing him to abandon the other claims he wished to preserve for appeal.