Page last updated at 08:45 GMT, Monday, 8 September 2008 09:45 UK

The case for forensic linguistics

By Elizabeth Mitchell
Science reporter, BBC News, Liverpool

WARNING: This graphic contains language that may offend

Text message analysis is becoming a powerful tool in solving crime cases.

In February 2008, linguistic evidence contributed to the conviction of David Hodgson in the murder of Jenny Nicholl.

The case highlighted how people choose their own text language "rules" - which they tend to use throughout all their messages.

Forensic linguists showed that text messages sent from Jenny's phone after she went missing had a style that was more similar to that of David Hodgson.

Jenny Nicholls' body was never found, but the jury accepted the prosecution's view that Hodgson had been sending texts on her mobile after her presumed death and found him guilty of murder.

The case is illustrative of what can be achieved by analysing mobile messages, said Dr Tim Grant from the Centre for Forensic Linguistics at Aston University.

He is speaking here in Liverpool at the British Association Science Festival.

Dr Tim Grant explains forensic linguistics

Identifying the author of an anonymous text message might seem like an impossible challenge as they are typically very short and fragmented.

Traditionally, forensic linguists use a descriptive approach.

They demonstrate that there are several stylistic features that are consistently used in messages where they know the author.

For example, Jenny Nicholl used "my" and "myself" while David Hodgson often adopted Yorkshire dialect, using "me" and "meself."

Forensic linguists look to see whose style is most similar to that used in any disputed texts.

Text database

Dr Grant has developed a method to quantify linguistic evidence that can be later used in court.

"You have show expertise over and above that of the average jury member - we're all language experts," he told reporters.

He has built a specialised language database of over 8,000 text messages and analysed them using robust statistical methods that he has adapted from those originally developed by forensic psychologists investigating sexual crimes.

"Collecting the data is a continuous process - language changes and moves on all the time," said Dr Grant.

Forensic linguists rely on police evidence to constrain the number of possible authors: "As the numbers grow the statistical power weakens," explained Dr Grant.

During his lecture at the BA Science Festival in Liverpool on Monday, Dr Grant will collect and analyse text messages from audience members.

Forensic linguists can also build a "sociolinguistic" profile of the author: they can give an idea of a texter's gender or age - but not their personality.

"What you find is very stereotypical - women tend to be inter-personal while men make arrangements," said Dr Grant.

"The more features I can reliably move into a personal description - the more powerfully I can discriminate," he added.

On 1 September 2008 the Council for the Registration of Forensic Practitioners - a government-based body which promotes confidence in forensic practice - recognised forensic linguistics as a speciality.

"This is external validation that forensic linguistics is moving from an expertise-based opinion into the scientific field," said Dr Grant.


SEE ALSO
Reading between the lines
23 May 08 |  West Midlands
Man guilty of teenager's murder
19 Feb 08 |  North Yorkshire
Texting study to catch criminals
11 Aug 06 |  Technology

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