CSI: Chatroom

In October 2008, two teenagers log on to the web messaging service MSN. "Wots that THING in ur s/n," types the first, 18-year-old East London rapper Kingsley Ogundele, speaking in a mixture of Jamaican patois and online slang. "Just Playboy shit," replies his friend and fellow grime artist Brandon Jolie, also 18. "Lmao," replies Jolie. Later in their conversation, Ogundele moves disturbingly quickly from such banter to planning a murder. He refers to his intention to kill a schoolgirl pregnant with Jolie's unborn baby – who the pair believe is giving Jolie undue hassle. "I'll get da fiend to duppy her den," he writes.

We have The Wire to thank for our knowledge of American drug-dealing slang – "corner boy" is a gang-member keeping watch on behalf of drug dealers, for example. But what about in the UK? Well, these days – eight years after The Wire came to prominence – British cops have their hands full deciphering a different form of language, that which combines street slang with dialects evolving to take advantage of advances in online technology. As such, language experts working with the police have their hands full keeping up with the change in people's conversational styles. Thankfully the online tools exist to help them do it.

The above exchange between Ogundele and Jolie is case in point. To give you the background: in December 2008, two months after the conversation above, the girl pregnant with Jolie's baby was lured by text to a spot close to the Regent's Canal in Islington, North London. There, Ogundele lay in wait to batter the girl over the head with an iron bar before throwing her in the waterway. Both the girl and the baby escaped alive, and the search turned to her assailant. After Ogundele and Jolie became prime suspects, their computers were seized. They had forgotten to delete their MSN history folders and police called in experts from the University of Aston's Centre for Forensic Linguistics. They helped decipher the boys' language, and the two rappers were sentenced for conspiracy to murder last month. Ogundele got 18 years in prison, Jolie, 14. So how did they do it? Tim Grant, the centre's deputy director, was one of those compiling a "dictionary" of the terms used by the two rappers.

"We work a lot with electronic communications of various sorts," he says. "It's familiar to us, so we're often called into cases that involve it." "S/n" is commonly observed online to mean "screen-name". Equally, it doesn't take much to figure out that "lmao", means "laughing my ass off". But what about "da fiend" and "duppy"?

Grant says his first port of call was traditional hard-copy dictionaries like the Oxford English. But because the boys were communicating online, he soon had to turn his attention to online dictionaries that are more likely to keep place with frequent changes in slang. For this, there are those that specialise in Jamaican dialect, such as thedialectdictionary.com, or popular slang websites like urbandictionary.com. "There are slightly ironic travellers' dictionaries which you can draw on [gypsy-jib.com], alongside more serious linguistic dictionaries," he continues. "But with the online dictionaries you have to be sceptical about their quality. Many of them are Wikis [dictionaries whose entries users can change themselves], so there is no quality assurance. You need to find four of five examples of the words being used in the same context to feel any kind of security in their usage."

In the case of "da fiend", several online dictionaries – including urbandictionary.com – cite this as meaning "drug fiend" (a drug addict of either crack or heroin). But what about "duppy"? "In this case I had to try and find the word used in a web forum or on web pages," Grant continues. "Linguists generally say that if you find enough examples of something being used then that's generally what it means. With the word 'duppy' I could find several examples of it being used as a noun, meaning 'death', online. It is a word used to mean a 'ghost' in Jamaican English. Because they were grime musicians from East London I went to various East London grime blogs. There were a few examples of 'duppy' being used as the verb 'to kill' so I could make the tentative conclusion that this is what it meant."

The word "duppy" has also leaked into video gaming culture: "duppies" appear as common enemies in the 2002 video game Shadow Man (for the Nintendo 65 and Sony PlayStation consoles). In fact "duppy" was an English word for ghost in Elizabethan times although some dictionaries cite an African origin. Either way, it is clear that the suspects intended to make a ghost of their victim. Grant compiled a long glossary explaining all of the boys' language which he submitted to the jury considering the case.

According to online security experts Symantec, planning a murder on a popular online messaging programme is rare – the vast majority of online crimes relate to the advertisement of stolen credit card details. The firm's experts believe that instead of using coded language, cybercriminals are much more likely to communicate in traditional English. They can afford to do this because they tend to use secure means of communication like Internet Relay Chat – a form of instant messaging – to make sure they remain undetected. "The big guys tend to hide themselves away a bit more – they get their associates to do their dirty work for them," says Orla Cox, a Symantec security researcher. However Cox indicates that acronyms that the general public may be unfamiliar with are still used in such situations. These include "Fullz CC" to mean full credit card information or "CVV" which refers to the number encoded on the magnetic strip of credit cards (which is used to authorise their transactions – useful to know if you're buying a stolen credit card).

When not analysing language used online, Grant may turn his attention to other technological language – specifically "text speak". His analytical methods are so advanced that he can often analyse a style of text message and work out who is sending it. He describes a recent case he worked on – whose protagonists he cannot name for legal reasons – where a man murdered his partner before setting fire to the house they shared. After killing his partner he sent a series of messages to her friends and family, posing as her, trying to pretend that she was going to go to bed early with some aromatherapy candles. By analysing the texts, Grant could prove that they were in fact sent by him – having killed her, and about to set the house on fire – as opposed to her.

"As part of the evidence assembled for the case the police went around all of the lady's friends and family collecting the text messages which they had received from her phone," explains Tim Grant. "When we began to check this history of messages we could assemble a pattern of use. The earlier ones were indisputably sent by her. But at some time during the day before the fire, a change in style suggested the text messages were being sent by the suspect, instead of the deceased. He said, 'dont', for example, whereas she always wrote, 'don't', with the apostrophe. If you get seven or eight examples of the husband and wife using each spelling, while not particularly statistically significant, it does suggest a certain pattern of use." Such knowledge, combined with data from the house burglar alarm – which suggested there was movement in the house after the wife was killed – managed to convict the husband.

"It could be argued that breaking through anonymity in writing is yet another encroachment on civil liberties," he concludes. "But being able to analyse these short and fragmentary electronic messages is hugely useful to investigators. And in the novel context of mass anonymity that the explosion in the number of electronic messages provides, these techniques are a tremendous social good."

Slang warfare: A crime online

2 Snoops ["Snoopy Montana" or Kingsley Ogundele]: wots that THING in ur s/n.

Grant's translation: What's that thing in your name?

His explanation: "s/n" is an abbreviation for screen name.

2 Snoops: wen u see da beam on her head you do da b.

Grant's translation: When you see the beam on her head you get out of there.

His explanation: "Beam" as in laser beam from a gun sight. "Do da b" – do the b indicates to skip a song on a music player and associated with this is a meaning to skip out or do a bunk. Other possible interpretations would include "do the business" or "do the bitch".

2 Snoops: we will go and post up.

Grant's translation: We will go and post up.

His explanation: "Post up" is to stand at a spot (eg a street corner or lamp post) to claim as territory or as an observation spot. Originates in slang used by drug-dealers.

2 Snoops: ill get da fiend to duppy her den.

Grant's translation: I'll get the addict to duppy her then.

His explanation: A duppy is a ghost in Jamaican folklore and has spilled over into some video gaming indicating zombies and "undead" characters, so this may mean kill or harm. It is unusual but not unheard of to find it used as a verb.