How the Unabomber’s unique linguistic fingerprints led to his capture

Can the language someone uses be as unique as their fingerprints?

As I describe in my forthcoming book, “Linguistic Fingerprints: How Language Creates and Reveals Identity,” that was true in the case of Theodore Kaczynski.

Kaczynski, who was known as the Unabomber, died in a North Carolina prison on June 10, 2023, reportedly by suicide.

Kaczynski had been a math prodigy and a professor at the University of California, Berkeley, before he withdrew from society and declared war on the modern world.

From a remote cabin in Montana, he sent a number of explosive devices through the mail. In other cases, he planted them. Between 1978 and 1995, 16 of his bombs killed three people and seriously injured nearly two dozen more.

Kaczynski’s crimes triggered the longest and most expensive criminal investigation in U.S. history. Law enforcement had little to go on other than a few letters that the terrorist had sent to the media, as well as fragments of notes that had survived his device’s detonations.

Spellings and word choices offer clues

In 1995, there was a breakthrough. That’s when the Unabomber offered to pause his attacks if a newspaper published his manifesto about the evils of modern society. Controversially, The Washington Post did so. The FBI supported the paper’s decision, hoping that someone would recognize the terrorist based on the writing style of the 35,000-word essay.

FBI forensic linguist James Fitzgerald and sociolinguist Roger Shuy were able to uncover several clues about the terrorist’s identity based on the manifesto and his other writings.

For example, the Unabomber used strange misspellings for some words, such as “wilfully” for “willfully,” and “clew” for “clue.” Shuy recognized these as spelling reforms that had been championed by The Chicago Tribune during the 1940s and 1950s, although they were never widely adopted.

Their use by the bomber suggested he might have spent his formative years in or near Chicago.

Fitzgerald noted the use of terms like “broad,” “chick” and “negro” in the manifesto was consistent with the vocabulary a middle-aged person from that era.

The Unabomber also referred to “rearing children” as opposed to “raising children.” The former term is characteristic of the northern U.S. dialect and would be consistent with someone who grew up in or near the Windy City.

The manifesto also contains such fairly esoteric terms as “anomic” and “chimerical,” suggesting that its author was highly educated.

A brother’s suspicions

But the move to publish the manifesto ended up being the decisive factor.

It was read in Schenectady, New York, by Linda Patrik, who showed it to her husband, David Kaczynski. She asked if he thought it sounded like something his brother Ted could have written.

David was initially skeptical. Then he noticed that the essay contained unusual expressions, like “cool-headed logicians,” that he remembered his estranged sibling making use of. He approached the FBI with his suspicions, and it was noted that David’s brother had been born in Chicago in 1942.

A search of Kaczynski’s cabin turned up explosive devices, as well as the original copy of the manifesto. Kaczynski pleaded guilty in 1998 and was incarcerated until his death at age 81.