N.H. Rev. Stat. § 613-A:6
If a person confined in a penal institution in any other state may be a material witness in a criminal action pending in a court of record or in a grand jury investigation in this state, a judge of the court may certify (1) that there is a criminal proceeding or investigation by a grand jury or a criminal action pending in the court, (2) that a person who is confined in a penal institution in the other state may be a material witness in the proceeding, investigation, or action, and (3) that his presence will be required during a specified time. The certificate shall be presented to a judge of a court of record in the other state having jurisdiction over the prisoner confined, and a notice shall be given to the attorney general of the state in which the prisoner is confined.
RSA 613-A:6
1959, 83:1, eff. July 5, 1959.