Forensic Linguistics

Forensic linguistics is the art of extracting meaning from language. It is a multifaceted discipline that explores phonetics (the system of sounds in a language), syntax, dialectology (variations in language based on regional boundaries), semantics, and psycholinguistics (how the human brain processes language).

Forensic linguists perform language analysis on spoken or written documents to identify the author or determine whether two documents have the same author. Forensic linguists can analyze ransom notes, suicide notes, anonymous letters, scamming calls, wills, courtroom transcripts, emails, texts, and police interview transcripts. Longer documents are easier to analyze as they tend to exhibit clearer and more identifiable writing and word patterns. Forensic linguists don’t just work behind the scenes – in courtroom settings, they can be used to predict how witnesses will likely respond to questions based on an analysis of courtroom language and questioning, and work with lawyers to interpret what the semantics of a written law could mean for a person’s verdict.

Forensic linguists work with law enforcement, under the Foreign Service, FBI, CIA, or Department of Justice, or privately as consultants to law firms. They use their knowledge of foreign cultures, languages, and dialects to ensure correct interpretation of spoken and written language and identify criminals that could pose an international threat to the US, such as in cases of terrorism or espionage.

In their analysis of linguistic style, forensic linguists may use several methods: in the case of comparative linguistics, forensic linguists note changes or consistencies in vocabulary choice, wherein for instance, “greetings and sign-offs in emails could be compared.” When analyzing written documents, they might also compare spelling (English vs. American English spelling) and the format in which the date is written, with both primarily varying geographically. They note the use of capitalization, slang, and certain idioms and phrases. To further understand how a person’s location or background may be reflected in their use of language, forensic linguists use dialectology – primarily used in recordings, this is where a person’s accent is analyzed. Separately, “discourse analysis” is applied, wherein stutters, filler words, and backchanneling are observed to give clues on how the person may normally converse.

One of the most notable cases where forensic linguistics was used was that of the Unabomber. For 17 years, starting from 1978, Theodore Kaczynski mailed bombs to several universities and airlines, killing 3 and injuring over 12 more. After careful “forensic examination of recovered bomb components” and of the lives of the victims yielded no results, the FBI decided to allow the Washington Post and other news outlets to publish Industrial Society and its Future (FBI). This was a manifesto written by the suspect about his motives behind the bombings – largely stemming from his discontent with modern society and technology – which he demanded to be published. Soon, a reader was able to identify the author just as the FBI hoped – David Kaczynski, who recognized “the word choices and philosophy resembled those of his brother” (Crime Museum). Specifically, a specific phrase stood out – Theodore writing “eat your cake and have it too,” a common reversal he made of the Modern English proverb “have your cake and eat it too.” After providing investigators with more letters and documents authored by his brother, forensic linguistics were able to closely examine the philosophical statements made and confirm that Theodore Kaczynski was the author of the manifesto, and their evidence finally convinced the judge to issue a search warrant of Kaczynski’s cabin.

Forensic linguistics have also been an important asset to people who don’t understand English well – from standardizing the Miranda rights to ensure that it can be effectively translated for people who don’t know English, and the overturning of the conviction of Gene Gibson, an aboriginal Australian who was incriminated by a police interview conducted in English, despite English being his third language.

Forensic phonetics is a subfield of forensic linguistics that deals with sound recordings – phonetics is defined as “the art/science of the description of the sounds of speech” (Office of Justice Programs). And while the “science of speaker identification will never reach the degree of certainty associated with the matching of fingerprints or DNA profiles,” forensic phonetics does require thorough analysis, focusing acoustical sounds, pronunciation, and grammar to identify a speaker. Through the collection of various markers, forensic experts may be able to develop a sort of “linguistic fingerprint.”

Alan Cooper, a senior forensic practitioner, discusses in a BBC interview that after being sure investigators have a good range of speech sounds made by the suspect recorded, voice recordings are investigated and polished further. When background music or chatter might obscure sound, investigators use signal processing to subtract that sound from the recording. The “hum” from electrical power sources is “embedded in digital recordings” – by extracting this sound, scientists can accurately determine the time and date of a recording and see whether it has been tampered with. Peter French, the Director of the Forensic Speech Laboratory in the UK, also reveals in the interview how investigators have mapped out the geographical distribution of the vowel and consonant sounds, using this information to provide a better understanding of a speaker’s background or origin.

Francis Nolan, a Professor of Phonetics at Cambridge University, elaborated how computer software is often used to isolate vowels out of individual words in a recording for more precise analysis, while sound spectrograms – or graphs of the speech – are inspected for more details on the speaker’s average pitch. Forensic speech scientist Dr. Kirsty McDougall from Cambridge University further comments on how noticing hesitations and idiosyncrasies can also help with speaker recognition. She sheds light on other factors that may influence a recorded speech and make it harder for investigators to get a clear picture of a person’s true voice – for instance, a person who is using drugs or is drunk may sound different.

When a sound recording isn’t available, investigators rely on victims’ descriptions of the voice to arrange a “voice lineup.” However, it is hard to find voices similar to what a person might have described and then for the person to identify the voice. As time goes by, the reliability of a person’s voice recognition (especially of someone they might have had very little interaction with) decreases.

Forensic linguistics has also had to adapt to the internet landscape, as many documents are not written, recorded, and transmitted online, posing new challenges to identifying the author. This has largely meant a decrease in the analysis of handwriting and more attention to the other parts of linguistic styles, such as syntax, spelling, punctuation, and structure. They also look at identifiable information that may have been made public, such as the inclusion of a birthyear or real name in the username. In 2012, defaming posts were written online about Fred Heebe, a Louisiana attorney and businessman, who noted that the online troll knew insider information about the US Attorney’s Office. James Fitzgerald, a forensic linguist, noticed the repeated usage of the words “coil,” “dubiety,” and “redoubt,” left in the defaming posts of the anonymous writer – words which led him to a handful of court filings signed by US attorneys out of all the federal documents he considered. This eventually helped him narrow down the suspect list to Sal Perricone, the deputy US attorney to Heebe’s former opponent.

However, internet trolls can easily imitate and impersonate other people, which may cause linguists to falsely implicate someone. Since language is not unique to one person, linguistic profiling is still much less certain compared to DNA profiling. Efforts have been made to make the web less anonymous through forensic linguistics – Tim Grant of the International Association of Forensic Linguists is “building a collection of tweets to research regional language patterns in the U.S” (CBS News).

While forensic linguistics may never achieve the certainty of DNA profiling, its impact is undeniable. From unmasking the Unabomber’s manifesto author to ensuring accurate translations of rights, forensic linguistics has made its mark in discerning truth from deceit.

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