Persons who are deprived of their liberty (held in jail, prison, or a psychiatric institution) have the right to challenge the legality of their arrest or detention through a judicial inquiry or process known as habeas corpus. Habeas corpus is a centuries-old Latin phrase meaning “produce the body.” By means of a writ of habeas corpus, a court or judge may order the state to “produce the body”—in other words, to hand over the prisoner—so the court may review the legality of the prisoner’s detention.

For example, federal courts may use the writ of habeas corpus to determine if a state’s detention of a prisoner or other detainee—such as an institutionalized psychiatric patient—is lawful. A petition for writ of habeas corpus proceeds as a civil action against the state agent who is holding the prisoner in custody—usually a prison warden or psychiatric facility and treating psychiatrist.

State and federal prisoners often file a petition for writ of habeas corpus after their conviction to challenge the legality of federal laws that resulted in their detention. Habeas corpus petitions may also be used to challenge detention in immigration or deportation cases and military court detentions and convictions. And a habeas petition may be used to challenge preliminary matters in criminal prosecutions, such as (1) whether there is an adequate basis for detention; (2) removal to another federal district court; (3) the denial of bail or parole, or excessive bail; (4) the failure to provide for a speedy trial or hearing; (5) a claim of double jeopardy; (6) the legality of extradition to another state or a foreign country; or (7) the jurisdiction of the court. See 28 U.S.C. §2241.

Thus, the purpose of a writ of habeas corpus is not to determine the guilt or innocence of the detainee, but to test the legality of the current detention or confinement. It is a safeguard against imprisonment of persons detained in violation of the law—by requiring government authorities to provide valid reasons for the detention. If the habeas petition is granted and the writ is issued, it provides immediate relief from the unlawful detention by ordering the detainee be released from custody.

The right to petition for a writ of habeas corpus is guaranteed by the United States Constitution and by state constitutions.

In New Hampshire, as in all states, persons who are deprived of their liberty through detention in jail, prison, or a psychiatric institution have the right to challenge the legality of their arrest or detention via a judicial process known as habeas corpus. This process allows a court or judge to order the state to present the detained individual so that the court can review the legality of the detention. The petition for a writ of habeas corpus is a civil action against the state agent responsible for the custody, such as a prison warden or the head of a psychiatric facility. Habeas corpus petitions can be filed by state and federal prisoners after their conviction to challenge the legality of the laws that led to their detention, and they can also be used in immigration cases, military detentions, and to address preliminary matters in criminal prosecutions. The purpose of habeas corpus is to ensure that a person's detention is lawful, not to determine guilt or innocence. If a court grants the habeas petition and issues the writ, it can result in the immediate release of the detainee if their detention is found to be unlawful. The right to habeas corpus is enshrined in the United States Constitution and is also protected under state constitutions, including New Hampshire's.