appellate habeas corpus

in all cases where a Circuit Court of the United States has, in the exercise of its original jurisdiction, caused a prisoner to be brought before it, and has, after inquiring into the cause of detention, remanded him to the custody from which he was taken, this court, in the exercise of its appellate jurisdiction, may, by the writ of habeas corpus, aided by the writ of certiorari, revise the decision of the Circuit Court, and if it be found unwarranted by law, relieve the prisoner from the unlawful restraint to which he has been remanded.