The most recent version allows material witnesses to be held to ensure the giving of their testimony in criminal proceedings or to a grand jury.
Since September 11, 2001, the U.S. has used the material witness statute to detain suspects without charge for indefinite periods of time, often under the rubric of securing grand-jury testimony.
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."
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.
During and after that period, the overwhelming majority of material witness warrant hearings took place in judicial districts bordering Mexico and involved illegal alien traffic.
[citation needed] In 2009 the Ninth Circuit of Appeals in San Francisco, California found in Ashcroft v. al-Kidd that former Attorney General John Ashcroft could be sued personally for wrongful detention by Abdullah al-Kidd, an American citizen who was arrested in 2003 and held for 16 days in maximum security prisons to be used as a material witness in the trial of Sami Omar Al-Hussayen.