If there is anything I've learned about forensic linguistics, it is not to underestimate the power of language. This becomes evident in the Unabomber case in which Ted Kaczynski sent a series of mail bombs, maiming and killing several victims.
After years of pursuing the Unabomber through various tactics, a former Philadelphia policeman come FBI agent named James Fitzgerald worked incessantly, analyzing every scrap of Kaczynski's writing. Having no formal training in linguistics, Fitzgerald was able to pinpoint the oddities he found in his suspect's writing that defined his idiolect. For example, some letters included the seemingly backward phrase "have your cake and eat it too." Interestingly enough, this is how it was spoken at one time.
The search culminated with the Unabomber's Manifesto, which was published in the Washington Post. Ted Kaczynski's brother was one of the people to read the Manifesto, who provided more key evidence, resulting in Kaczynski's arrest at his Montana cabin.
Thirty years later, forensic linguistics has taken on more force with much more advanced technology. (Fitzgerald was doing all this by spreading pieces of paper on the floor!) Nevertheless, we all still have our own special and peculiar way of speaking and writing that can sometimes act as a fingerprint. With more and more of our data finding its way online, our linguistic fingerprints leave behind a veritable linguistic footprint.
Manhunt: Unabomber, an eight-episode miniseries is available on Netflix.