By analyzing syntax and linguistic patterns an expert can, on occasion, reach reasonable conclusions as to whether a particular individual authored a document. This can be a crucial matter in an internal investigation or in the defense of a crime. A lengthy recent article in The New Yorker Magazine (July 23, 2012, J. Hitt), entitled "Words on Trial", discusses the subject in an entertaining and informative way and would be helpful for the reader seeking more detail. Even if such analysis can't conclusively prove a specific person wrote a document or uttered a phrase it can be helpful in cutting down the number of suspects to a more easily investigated group.
The field of forensic linguistics received considerable attention in 1996 when it was partially responsible for solving the Unabomber case. Within a few days of publishing the Unabomber's Manifesto the FBI received tips from over a dozen people, including the Unabomber's brother, that the mode of expression, vocabulary and syntax of that document was similar to Ted Kaczynski's utterances. The Manifesto made repeated use of the terms "chimerical" "anomic" and "cool headed logicians" as well as the phrase "you can't eat your cake and have it too." People personally familiar with Ted Kaczynski immediately recognized these phrases as catchwords of his and the focus of the far ranging investigation was immediately and very effectively tightened to just him.
Historically, forensic linguistics has been used in a common sense way. In the Old Testament, at Judges12:6 an early use is made of forensic linguistics. In that passage it is recounted that after a melee between a tribe of Israel (the Gileadites) and their enemies (the Ephramites) a number of Ephramites attempted to pass as victorious Gileadites and make their escape from the battlefield. The Gileadites were able to unmask the posing Ephramites by forcing them to pronounce the Hebrew word "shibboleth". Ephramites apparently pronounced the first syllable "sib" unlike the proper Hebrew pronunciation of "shib". To quote the text, "If he say 'shibboleth' then they seized him and slaughtered him at the fords of the Jordan". Also historically in the Lindbergh Kidnapping case the prosecution made much of misspellings in the ransom note which matched errors made by the defendant Bruno Hauptmann in other contexts. The text of the kidnapping note to Colonel Lindbergh included, "We warn you for making anything public or for notify the Polise the child is in gut care." Hauptmann had misspelled "police" and used the German "gut" for good in other contexts.
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Today more sophisticated analysis is used. Perhaps most spectacularly, a computer generated word usage count was used to prove that Joe Klein of Newsweek was the author of the anonymously authored novel "Primary Colors" about the Clintons in the early 1990s. The vocabulary usage and statistically replicated syntax matched Klein's other works very convincingly. Recently in Harrisburg, a perjury prosecution was dropped by the district attorney based on an expert opinion by a forensic linguist concerning the actual meaning of a some testimony by a grand jury witness. In some cases a forensic linguistic expert can make all the difference.
A Communicate Threat Assessment Database has been established by a former FBI forensic linguist allowing for quicker analysis and comparison of criminal threats. Even in contexts short of outright criminality statistical analysis of linguistic pattern, word usage, syntax and the like can help establish the authenticity or authorship of a documents or statements. Forensic linguistics is a valuable tool to keep in mind in internal investigations and white collar criminal defense.