which convicted him. A showing in a return to a writ that the
prisoner was held under final process based upon a judgment of a court
of competent jurisdiction closed the inquiry.[1442] Under the Judiciary
Act of 1789[1443] the same rule obtained.[1444] But by the act of
February 5, 1867,[1445] Congress extended the writ to all persons
restrained of their liberty in violation of the Constitution or a law or
treaty of the United States, and required the Court to ascertain the
facts and to "dispose of the party as law and justice require." This
gave the prisoner a right to have a judicial inquiry in a court of the
United States into the very truth and substance of the causes of his
detention. The Supreme Court has said that there is "no doubt of the
authority of the Congress to thus liberalize the common law procedure on
_habeas corpus_ * * *" .[1446]

Habeas Corpus Not a Substitute for Appeal

Since the writ of _habeas corpus_ is appellate in nature, Congress may
confer jurisdiction to issue it upon the Supreme Court as well as upon
the inferior federal courts.[1447] The proceeding may not, however, be
used as a substitute for an appeal or writ of error.[1448] But if
special circumstances make it advantageous to use this writ in aid of a
just disposition of a cause pending on appeal it may be used for that
purpose.[1449] Where facts dehors the record, which are not open to
consideration upon appeal, are alleged to show a denial of
constitutional rights, a judicial hearing must be granted to ascertain
the truth or falsity of the allegations.[1450]

Issuance of the Writ

On application for a writ of _habeas corpus_, the Court may either issue
the writ, and, on the return, dispose of the case, or it may waive the
issuing of the writ and consider whether, upon the facts presented in
the petition, the prisoner, if brought before it, could be
discharged.[1451] The proceeding may not be used to secure an
adjudication of a question which, if determined in the prisoner's favor,
could not result in his immediate release.[1452] A discharge of a
prisoner on _habeas corpus_ is granted only in the exercise of a sound
judicial discretion.[1453] While the strict doctrine of _res judicata_
does not apply to this proceeding,[1454] the Court may, in its
discretion, dismiss a petition for _habeas corpus_ where the ground on
which it is sought had been alleged in a prior application, but the
evidence to support it had been unjustifiab