18 U.S.C. § 3144 : US Code - Section 3144: Release or detention of a material witness

      If it appears from an affidavit filed by a party that the
    testimony of a person is material in a criminal proceeding, and if
    it is shown that it may become impracticable to secure the presence
    of the person by subpoena, a judicial officer may order the arrest
    of the person and treat the person in accordance with the
    provisions of section 3142 of this title. No material witness may
    be detained because of inability to comply with any condition of
    release if the testimony of such witness can adequately be secured
    by deposition, and if further detention is not necessary to prevent
    a failure of justice. Release of a material witness may be delayed
    for a reasonable period of time until the deposition of the witness
    can be taken pursuant to the Federal Rules of Criminal Procedure.