A BRANCH of forensic science which analyses the electronic trail of evidence left by text messages and e-mails is increasingly being used by police to trap criminals.
British scientists are pioneering the use of forensic linguistics – the systematic analysis and comparison of patterns of written speech – to identify the authors of electronic messages and written documents.
The technique helped secure the conviction of the murderers of Essex schoolgirl Danielle Jones, 15, and Jenny Nicholl, 20, from North Yorkshire, and of al-Qaeda plotter Dhiren Barot.
Now scientists at the Centre for Forensic Linguistics at Aston University, Birmingham, say they are overwhelmed by requests from the police for help.
"We've seen a massive growth in casework, particularly in the area of electronic communication – SMS text messages, internet relay chat and e-mail – and our track record over the past ten years has shown it can be effective," Dr Tim Grant told the British Association for the Advancement of Science yesterday.
"It's particularly useful in difficult cases where … there's no physical crime scene."
Tomorrow, Dr Grant gives the Joseph Lister Award Lecture at the association's Festival of Science in Liverpool and will over the next two months submit evidence for trials in the US, Australia and South Africa.
He said this kind of evidence was bound to become more important: "There's been a massive growth in people writing to one another using phones, computers or electronic gadgets.
"In these situations it's easy to be anonymous, or at least feel you are anonymous, and while traditional police forensics can trace back and tell you where a phone was when a call was made, it can't tell you who was holding it and that is where forensic linguistics is proving so useful."
The key to determining authorship of messages or written documents is to identify patterns in style – spelling, punctuation and use of language, as well as the spacing between words – and the frequency of functional words such as "of", "if" and "the".
"What you need to demonstrate authorship is consistency in style and distinctiveness in style," said Dr Grant.
"What you have to do is ask the investigator to go away and find more examples of written documents or texts and more examples in similar genres – and that can be really tricky because we all change our style depending on who we are writing to, how formal the text is, what the context is and so on."
Evidence from Dr Grant's colleague, Professor Malcolm Coulthard, helped secure successful appeals against the conviction of the Bridgewater Four, finally released in 1997, and Derek Bentley, who was hanged in 1952 for his part in the murder of PC Sidney Miles.
Increasingly the technique is also being used for more mundane police investigations.
"What seems to be happening is that even in relatively minor car accidents police will scoop up mobile phones as being good evidence … in some of those cases you will find there's a question of who was holding the phone when something was sent," said Dr Grant.
Similar linguistic analysis methods have been used in recent years to help determine authorship of disputed historic texts, including novels and a disputed Shakespeare play.