Ted Kaczynski's manifesto. The ransom note for Jon Benet Ramsey. The anthrax letters threatening our government and media agencies. With the aid of forensic linguistics, the words criminals leave behind in their unsigned letters can be as distinctive as a signature or voice. Although the linguistic study of language is well established, this important analytical tool is something new for many jurors, judges, attorneys, and other forensic specialists dealing with both criminal and civil cases.