In an episode of the CBS show Criminal Minds that aired last year , an FBI team is on a frantic hunt for a missing 4-year-old. The team soon realizes that the girl has been given away by a relative, Sue, and that theres no way Sue is going to reveal her whereabouts.

A crucial break comes when FBI profiler Alex Blake puts her word wisdom to work. Blake, who is also a professor of linguistics at Georgetown University, notices that Sue uses an unusual turn of phrase during an interview and in a written statement: I put the light bug on.

The FBI team launches an Internet search and soon discovers the same misuse of light bug for light bulb in an underground adoption forum: Ill switch the light bug off in the car so no one will see.

Same author, right? On that assumption, the team springs into action and bingo! the missing child is found.

Inspiration for Blakes expertise came from former FBI special agent and linguist James R. Fitzgerald, who became an adviser to Criminal Minds in 2008. Blake, he says, is a combination of him and his fiancee, Georgetown associate linguistics professor Natalie Schilling.

The incident, Fitzgerald says, is based on a 2008 homicide case, State of Alabama v. Earnest Stokes. In a linguistic report he prepared for the prosecution, Fitzgerald said he found the term light bug in an anonymous letter attempting to lead investigators off the track (His [sic] had busted the light bug hanging down) and in a tape-recording of suspect Earnest Ted Stokes. That was one of the lexical clues leading Fitzgerald to opine with a likelihood bordering on certainty that Stokes was the author of the unsigned letter.

The [Criminal Minds] writers love these real-life examples, Fitzgerald explains in an e-mail.

Thats not surprising. As more of our communication is written, the linguistic fingerprints we leave provide enticing clues for investigators, contributing to the small but influential field of forensic linguistics and its controversial subspecialty, author identification.

The new whodunit is all about who wrote it.

Answering that question becomes ever more urgent as we create a virtual trove of data in e-mail, in texts and in tweets that are often anonymous or written under pseudonyms. Private companies want to find out which disgruntled employee has been posting bad stuff about the boss online. Police and prosecutors seek help figuring out who wrote a threatening e-mail or whether a suicide note was a forgery. A groundbreaking murder case in Britain was decided after a linguistic analysis suggested that text messages sent from a young womans phone after she went missing were more likely to have been written by her killer than by her. And in Johnson County, Tenn., the outcome of the April Facebook murders trial may well hang, according to Assistant District Attorney General Dennis D. Brooks, on whether a linguist can convince jurors of the authorship of a slew of e-mails soliciting murder that were written, he says, under a fictitious name.

The rest is here:
Should texts, e-mail, tweets and Facebook posts be the new fingerprints in court?