Forensic linguistics and Forensic Phonetics in criminal investigation
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Every individual possesses unique fingerprints and almost unique DNA. Fingerprints and DNA profiles are the twin holy grails for law enforcement when investigating crimes and for prosecutors seeking to prove their cases. But humans can also be distinguished from each other by the way they speak and write.
Forensic linguistics is a discipline that concerns the analysis of written and spoken language for legal purposes. Forensic phonetics concerns the scientific properties of speech, including sound wave frequencies. Forensic linguistics and forensic phonetics are now frequently used in criminal investigations to identify suspects, eliminate suspects and to confirm authorship of written material. Linguistic evidence is regularly presented in court by both prosecution and defence lawyers.
Linguistic experts analyse written communications to make inferences about the author, including their age, regional origin and social standing. Practitioners examine the use of slang and dialect-specific vocabulary. They also explore spelling mistakes and grammatical errors. It may not be possible to identify exactly who has written the text concerned, but the field of suspects could be narrowed, and innocent parties could be eliminated from an inquiry. This form of analysis can help to establish if texts and emails were written by a missing person, a suspect or a third party. Plagiarism and fraud can be identified.
It is also possible to compare two or more communications to establish if they could have been written by the same individual. Communications can be compared to others of known authorship to assess linguistic similarities. Such comparisons can reveal whether a statement given in evidence was written by the witness or was written or altered by the police. For instance, numerous similarities between a statement and the relevant police incident notes could raise doubts about the veracity of the police record of an interview.
Between 1978 and 1995, Theodore Kaczynski, AKA the Unabomber, killed three people and injured 23 others. His identity was revealed after his family notified police when they recognised his writing style in a published article that became known as the Unabomber Manifesto. FBI linguistic specialists compared this text to confirmed examples of Kaczynski’s writing and found that they had been written by the same person.
Authorship identification has become increasingly important in recent years due to the huge rise in crime involving digital communications. Social media platforms facilitate fraud and hate crimes but enable perpetrators to remain anonymous. Analysis of written communications can help to identify the guilty parties.
Analysing speech with Forensic Linguistics
A speaker can be profiled by listening to samples of their speech to identify their regional accent and background. The infamous Yorkshire Ripper tape was analysed in this way. This tape was sent to the police by a man dubbed Wearside Jack. He confesses to being the Yorkshire Ripper in the recording. Experts were able to identify his accent as being distinctive to the Castletown area of Sunderland. On hearing the tape, linguists from the FBI immediately identified the tape as a hoax.
Unfortunately, the police believed it to be genuine, and this derailed the investigation for over a year, during which time the Ripper murdered three women. Wearside Jack was eventually identified via his DNA, and he did prove to be a native of Sunderland.
Two or more samples of speech can be compared to establish whether they are the same individual. Experts cannot absolutely confirm a match but will express a degree of certainly or doubt.
Recording analysis and transcription
It is relatively common for voice recordings to be offered as evidence in criminal proceedings. However, these recordings may be of poor quality and disputes then arise regarding exactly what was said. Phoneticians are often engaged to analyse disputed recordings to establish the exact words used in them. These experts will also transcribe recordings for evidential purposes.
Concerns about forensic linguistics
The services of forensic linguists have proved invaluable to law enforcement and crucial to the exoneration of innocent defendants. But how reliable is this form of investigation and evidence gathering?
There are several concerns surrounding the use of linguistic experts, and one of these is the lack of statutory regulation or accreditation. At the present time, in many countries, it would be possible for an underqualified or unqualified practitioner to masquerade as an expert.
There are limitations to forensic linguistics which jurors may not understand. Jurors seek certainty but this isn’t possible with linguistic and phonetic analysis. With DNA profiling an expert can quantify with amazing precision the likelihood of a profile belonging to a particular individual and no other. It is not possible for a linguistic expert to establish the likelihood of guilt or innocence with such precision. They will use loose expressions of probability such as “very likely” rather than those of certainty. The lack of qualitative conclusions can make it hard for juries to deduce the significance of the evidence.
Some forensic linguists have suggested that it would be possible to establish a linguistic fingerprint for each individual and to use this as evidence just as with an actual fingerprint. But most experts agree that while a linguistic fingerprint is an appealing thought, it would be impossible to rely upon this type of profiling.
The field of forensic linguistics will continue to evolve, and methods of analysis will be refined. The linguistic evidence of the future will be more precise and, therefore, easier to interpret. It will almost certainly become more reliable. For now, forensic linguistics does have a role to play in identifying and eliminating suspects. But any findings can only be viewed as circumstantial evidence and not as proof.