What Is a Material Witness in Legal Terms
A “material witness” is more or less a suspect in a criminal investigation. Maybe not a primary suspect. Maybe not even a suspect against whom criminal charges will eventually be laid. But a suspect who is quite important, “materially”, if you want to justify being detained for a certain period of time. Usually, law enforcement officers detain someone as a “material witness” when they fear that the person will escape their jurisdiction, but they do not yet have the property on that person to charge them with a crime. A substantive witness is a person who contains information that is “important” to criminal proceedings. With the authority of 18 U.S.C§ 3144, the U.S. government can request an arrest warrant from a bailiff to arrest a key witness. To do this, a U.S. official must file an affidavit with the bailiff alleging that (1) the person has important information about the criminal case and (2) that it would be “impossible to ensure the presence of the person by subpoena.” In 2009, the Ninth Court of Appeals in San Francisco, California. In ashcroft v. al-Kidd, it was concluded that former Attorney General John Ashcroft could be personally prosecuted for the unlawful detention of Abdullah al-Kidd, a U.S. citizen arrested in 2003 and held in maximum security prisons for 16 days to be used as a material witness in the trial of Sami Omar Al-Hussayen.
Al-Kidd was never charged or called as a witness. (Al-Husseini was acquitted of all charges of supporting terrorism in 2004.)   This led to controversy for several reasons. First and foremost, critics argued that the government`s use of the Background Witness Act to detain suspects was a circumvention of the Fourth Amendment to the U.S. Constitution, which provides criminal suspects with some protection that was apparently ignored during arrests of witnesses detained after September 11. Second, legal critics have opposed the application of the Status of Substantive Witnesses to grand jury proceedings. If an affidavit filed by a party indicates that the testimony of a person in criminal proceedings is important, and if it is shown that it may become impossible to ensure the presence of the person by subpoena, a bailiff may order the arrest of the person and deal with it in accordance with the provisions of article 3142 of this title. No substantive witness may be detained for failure to fulfil a condition of release if the testimony of such a witness can be adequately ensured by a statement and if additional detention is not necessary to avoid a breach of justice. The release of an important witness may be delayed for a reasonable period of time until the testimony can be given in accordance with the Federal Code of Criminal Procedure. In the current circumstances, however, I can imagine that longer “detentions” of trial witnesses may be admitted by judges, or at least not opposed by them. Who will tell the authorities in these frightening times that they should leave someone in the population who the Fed believes might have information about the worst crime in American history? And it seems to me that the longer a “material witness” is held in this case, the more likely it is that the person will eventually be charged.
Since September 11, 2001, the United States has used the Trial Witnesses Act to detain suspects indefinitely without charge, often under the guise of obtaining testimony before a grand jury. This application of the law is controversial and is currently subject to judicial review. In Ashcroft v. al-Kidd (2011), the detainee was never charged or called as a witness and sued the US government at the time. Attorney General John Ashcroft. The U.S. Supreme Court overturned a decision of the Ninth Circuit Court of Appeals and ruled that Ashcroft was eligible for immunity because of his official position. Statistics on hearings on substantial federal witness arrest warrants showed a steady decline from 2000 to 2002, from 3603 key witness hearings in fiscal year 2000 to 3344 in fiscal year 2001 and 2961 in fiscal year 2002. During and after this period, the vast majority of hearings with substantial witness arrest warrants were held in judicial districts bordering Mexico and involving illegal trafficking of foreigners.  Following the September 11, 2001 attacks, the U.S. government announced an aggressive campaign to detain those who may have been involved in attacks on the United States by any means possible.  The means included the use of the Status of Substantive Witnesses to arrest even suspects (as opposed to witnesses).
Many of those who have been imprisoned as material witnesses have been imprisoned as grand jury trial witnesses, who are merely investigating and not criminal trials. [Citation needed] A substantive witness is a person who is believed to have information about the subject matter of a prosecution that is decisive for the outcome of the case or trial ..