A material witness is an individual who contains information "material" to a criminal proceeding

Text of the Statute
18 U.S.C. § 3144, commonly referred to as the "material witness statute," provides as follows:

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.


[edit] Introduction
A material witness is an individual who contains information "material" to a criminal proceeding. With the authority of 18 U.S.C. § 3144, the United States government can seek a warrant from a judicial officer in order to arrest a material witness. To do so, a United States official must file an affidavit with the judicial officer alleging that (1) the individual has material information to the criminal proceeding and (2) it would be "impracticable to secure the presence of the person by subpoena."


[edit] "a criminal proceeding"
Although there has been much legal debate about the scope of the material witness statute, it has been clear since the Ninth Circuit Court of Appeals ruling in Bacon v. United States', 449 F.2d 933 (9th Cir. 1971), that the phrase "a criminal proceeding" from the material witness statute includes both trials (uncontroversially) and grand jury investigations. Thus, the ability to arrest material witnesses under the statute extends to the ability to arrest those with information material to a grand jury investigation (assuming the showing of impracticability is also made). The Supreme Court has not had a chance to rule on this statutory issue.


[edit] September 11 Controversy