If a critical document in a police investigation is unsigned and there are no credible suspects, how is its authorship to be investigated? This is the question considered in this paper. Nonlinguistic methods for investigating the authorship of a QD are few and sometimes misleading. Postmarks, addresses, and fingerprints on the document, as well as handwriting or typewriter evidence, are among the clues routinely examined by police. More recently, the analysis of trace DNA on stamps and envelope seals has been added to the repertoire of investigative tools. The language used by an unknown author may help investigators to establish the writer's age, gender, ethnicity, level of education, professional training, and ideology. Often, there is sufficient linguistic and textual evidence in a QD to establish the author's identity. When calling for scholarly assistance with a QD, police detectives should be prepared to provide the expert with an exact facsimile of critical documents, along with such additional materials as may be available and pertinent. Any original writing sample, whether handwritten, typed, or electronic, can help establish authorship of the QD; consequently, in a case that involves anonymous writing, search warrants should expressly include all reading material in the suspect's possession and all original writings in any form. Overall, police agencies and attribution scholars must work together to identify and pursue all avenues that can produce admissible evidence regarding authorship identification for anonymous QD's. 16 references