A material witness is a person who is presumed to have information about the subject matter of a lawsuit or criminal prosecution which is critical to the outcome of the case or trial. Thus, the court must make every reasonable effort to allow such a witness to testify, including a continuance (delay in a trial) to accommodate him/her if late or temporarily unavailable.
Under a 1984 federal statute, prosecutors may seek an arrest warrant if a potential witness's testimony is "material" to a criminal proceeding and the individual is likely to flee. A judge must approve the warrant, and the witness is entitled to a bond hearing and a court-appointed attorney. The limit of the bond amount varies by jurisdiction and the judge's discretion. Federal law requires that authorities get a judicial officer's permission to hold a material witness for any length of time. Release of a material witness may be delayed for a reasonable period of time until trial testimony or the deposition of the witness can be taken pursuant to the Federal Rules of Criminal Procedure.