As David Hodgson begins an 18-year prison sentence for killing Richmond teenager Jenny Nicholl, Joe Willis talks to the forensic linguistics expert whose pioneering work brought him to justice

NINE days after Jenny Nicholl was murdered, her killer David Hodgson sent messages from the teenager's mobile phone to two of her friends. Five days later, he sent another text to her father.

The messages were an attempt to suggest to police and her family that the 19-year-old was still alive.

However, when Hodgson was eventually brought to trial for Jenny's murder, the texts became key pieces of evidence for the prosecution.

Detectives say they suspected from the beginning that the messages were not sent by Jenny. But how did they prove this in court?

In a first for the region, Detective Chief Superintendent Sue Cross, the senior investigating officer, in the Jenny Nicholl case, and her team turned to forensic linguist Professor Malcolm Coulthard, who has given evidence at a number of high-profile court cases, including successful appeals against conviction of the Bridgewater Four and Derek Bentley, who was hanged in 1952 for his part in the murder of PC Sidney Miles.

Police investigating Jenny's disappearance gave the professor transcripts of the three July messages, plus more than 100 sample texts sent by the accused and 11 sent by Jenny.

Prof Coulthard says: "The interesting thing about text messages is that they're very short, but because it's a new way of working, people partially make it up themselves.

This makes text messages much more distinctive than other types of writing."

The professor's first step was to establish if there was evidence Jenny had sent the three mystery texts. At a glance, the texts looked like they could have been sent by the 19-year-old. The recipients later told the court they had their doubts about their authenticity, but the messages looked genuine enough for Ann Nicholl, Jenny's mother, to go looking for her daughter at the places they were sent from.

Under closer scrutiny by the professor, however, differences were found. When he examined the texts, he noticed that both Jenny and the sender of the mystery texts used the number "2" in place of "to". However, while Jenny left no space between the "2" and the following word, the sender of the mystery texts did, for example in the phrase "ave 2 lve".

Other differences were more obvious. While Jenny usually wrote "Im" and "Im not" in her texts, the mystery texts featured "I am" and "aint". When Jenny would use "my", "cu" and "fone", the words "me", "cya" and "phone" would appear in the July texts.

"I was able to say that it was highly unlikely she sent those text messages," Prof Coulthard says.

He then attempted to determine if there was evidence Hodgson had sent the three texts. To do this, he used the defendant's sample texts, plus two suicide notes he had left, as well as notes from writing exercises Hodgson carried out at the request of detectives.

A number of similarities with the mystery texts were found. The mis-spelling of the word "off", using one "f" rather than two, featured in a suicide note and the July texts. During the writing exercise, Hodgson even asked a police officer for help to spell the word. The word "might" was also mis-spelt as "mite" in the mystery texts and Hodgson's examples.

Matching abbreviations such as "aint" and "didnt" were also found in Hodgson's texts and those sent from Jenny's missing mobile.

Prof Coulthard says: "From a linguistic point of view, what I couldn't say was he sent those text messages'. But what I could say was he shared a lot of the same features and was among a small number of possible senders'."

The professor says that the unusual shared characteristics between Hodgson's texts and the mystery texts meant the number of possible senders was reduced.

His conclusions led prosecutors to tell the jury that Hodgson had attempted to mimic Jenny's texting style, but had made mistakes because he was rushing, or he had not studied her style sufficiently.

Prof Coulthard accepts that his evidence on its own was not overwhelming. However, he says its importance increased when used in conjunction with other testimonies.

Jenny's friends told the court that they did not understand some of the references in the texts. And the teenager's mother said she used to work in Richmond police station and her daughter would have more respect that to call police "pigs".

Later in the trial, a witness from the O2 mobile phone company revealed that the texts to Jenny's friends were sent from Brampton in Cumbria on July 9. The message to her father was sent from Jedburgh, in the Scottish Borders, on July 14, he told the court.

Records from a car hire firm were then produced.

These showed that Hodgson had taken out a hire car over the periods the texts were sent. When the mileage records of the hire cars were examined, they fitted roughly with the distances there and back to the locations where the messages were sent from. The prosecution told the jury this all had to be more than just an unhappy coincidence for the defendant. They agreed and unanimously found him guilty of killing Jenny.

As Hodgson begins his sentence of a minimum of 18 years he may well reflect that, had he not sent the messages, he may well have got away with murder.

Texts from a killer

Sent to Jenny's friend Jennifer Whelan on July 9, 2005"hi jen tell jak i am ok know ever 1s gona b mad tell them i am in scotland wiv my boyfriend.shitting meself dads gona kill me mum dont give a shite.hope nik didnt grass me up.keeping phone of.tell dad car jumps out of gear and stalls put it back in auction.tell him i am sorry"

Sent to Jenny's friend Nicola Gosnold at 12.16pm on July 9, 2005 "Thought u wer grassing me up.mite b in trub wiv me dad told mum i was lving didnt giv a shit.been2 kessick camping was great.ave2 go cya"

Sent to Brian Nicholl, Jenny's father on July 14, 2005

"Y do u h8 me i know mum does.told her i was goin.i aint cumin back and the pigs wont find me.i am happy living up here.every1 h8s me in rich only m8 i got is jak.txt u couple wks tell pigs i am nearly 20 aint cumin back they can shite off She got me in this shit its her fault not mine get blame 4evrything.i am sorry ok just had 2 lve shes a bitch no food in and always searching me room eating me sweets.ave2 go ok i am very sorry x"