In a purported class action to challenge the constitutionality of 8 U.S.C. section 1226(c), the section of the Immigration and Nationality Act that requires the mandatory detention of aliens who have committed specified crimes, the District Court's judgment is vacated where the District Court: 1) exceeded its jurisdiction by adjudicating the merits issues; and 2) adopted a doctrine of 'necessity' to deny class certification instead of analyzing the criteria enumerated in Rule 23 of the Federal Rules of Civil Procedure.