FBI sketch of D.B. Cooper (Oregonian file)

Consider for a moment the possibility that the skyjacker known as D.B. Cooper survived his perilous, 10,000-foot-high leap from a Boeing 727 and escaped into the rainy, wind-whipped night. He'd surely want to crow about it, right?

A former Army code-breaker believes the infamous criminal did boast about his success -- and that, nearly 47 years after the crime, this has led to him being revealed.

Rick Sherwood, recruited by longtime Cooper-case investigator Thomas Colbert, spent last winter and spring examining apparent ciphers in decades-old "D.B. Cooper" letters sent to newspapers. Sherwood says he deciphered the codes -- and in the process proved that the skyjacker is a 73-year-old former Vietnam War paratrooper named Robert Rackstraw.

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Robert Rackstraw (Courtesy of Tom Colbert)

When Colbert announced Sherwood's breakthrough earlier this year, it created a mini media frenzy, with the news taking off on social media and Cooper-case hobbyists around the world clamoring for more information. So now Colbert has publicly released both the codes and Sherwood's decoding system to allow anyone who's interested to reach their own conclusions.

The result: Two cryptology experts consulted by The Oregonian cast doubt on Sherwood's code-breaking.

"His decoding methodology allows too many totally arbitrary degrees of freedom," Oregon State University computer-science professor Mike Rosulek says. "So he is basically guaranteed to find anything he sets out to find."

Mathematician and cryptologist Lawren Smithline, who in 2009 cracked a 200-year-old code that had stumped Thomas Jefferson, said the process Sherwood used in decoding the Cooper messages was "simple English gematria" -- essentially a wordplay game. "As far as the D. B. Cooper case, the process has no value in determining reality," Smithline says. "If the wrong numbers came out, the solver could try endless combinations and tweaks to find the number desired."

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D.B. Cooper -- the unknown skyjacker actually bought his plane ticket under the name "Dan Cooper" -- became a folk hero shortly after he disappeared into the clouds on Nov. 24, 1971, with $200,000 in ransom strapped to his body. His takeover of Northwest Orient Flight 305 out of Portland remains the only unsolved commercial-airline hijacking in U.S. history.

In the months after the crime, a wave of letters arrived at newspapers around North America purporting to be from D.B. Cooper. The first one landed at Nevada's Reno Gazette. It praised the city's hospitality. Another went to a Vancouver, B.C., newspaper. In that dispatch, Cooper declared he had enjoyed watching the Canadian football championships on TV. A memorable letter arrived at The Oregonian, stating that his heist was "the system that beats the system."

The FBI dismissed most of the messages as ridiculous hoaxes, but there were a few that the bureau took seriously, mainly because they mentioned some detail about the skyjacking that hadn't been publicized.

Those letters, released to Colbert last year thanks to his persistent Freedom of Information Act requests, include what might be secret codes. Examples:

717171684*

7698QA2753

ccccccc

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The skyjacker leapt from the Boeing 727's apt stairs. (Oregonian file)

The FBI apparently couldn't figure out the seemingly random letters and numbers, and it closed the Cooper case in 2016. (The bureau has stated that it believes the skyjacker most likely died the night of the crime, either from the perilous skydive or from exposure in the vast Northwest forest.)

But Sherwood, using a basic letter-counting cryptography system (A=1, B=2, etc.), is convinced he successfully unraveled the letters' hidden meaning, not only for the standalone ciphers in the letters but also in the text of the letters. His accomplishment, he believes, comes from the fact that he knew what to look for. Colbert had already identified Robert Rackstraw as his suspect before Sherwood reviewed the potential ciphers. Colbert published a 2016 book about the retired college professor called "The Last Master Outlaw" and produced a TV documentary about the case.

Back in the late 1970s, when the FBI considered him a suspect, Rackstraw gave oblique, teasing answers when reporters asked him if he were the skyjacker. In recent years, he has denied that he's D.B. Cooper. (Rackstraw, who lives in the San Diego area, hasn't responded to The Oregonian's emails or phone calls.)

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A letter to The Oregonian that was turned over to the FBI in 1972.

When he began his decoding attempts, Sherwood looked for information that specifically related to Rackstraw. Soon, he found the former paratrooper's military units -- the 11th General Support Company and the then top-secret 371st Radio Research Unit and Army Security Agency -- hidden in some of the letters to newspapers.

Sherwood had to be creative to find Rackstraw in the messages. In a 1972 "Cooper" letter to The Oregonian, the Indiana resident discovered what he believes is a confession, turning the sentence "And please tell the lackey cops D.B. Cooper is not my real name" into "I'm LT Robert W Rackstraw." To decipher a different message that used letters cut out of Playboy magazine, he tracked down a copy of the issue (June 1970) and ended up finding a "code within a code." By subtracting the letters of the name of that month's Playmate from the cut-out message, he came up with, "I HAVE POB AND CODE WILL GO DOWN PM." Colbert and Sherwood suspect this is Rackstraw communicating with accomplices.

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Tom Colbert's explanantion of Rick Sherwood's decoding work. (Tom Colbert)

But Rosulek and Smithline believe that Sherwood's creativity is why he probably went astray.

"There is no way this [decryption method] was ever a method used in military cryptography," Rosulek told The Oregonian. "It's not systematic. He's imagining some encryption method that is not really an encryption method. That is the most fundamental thing. The criteria for success is so arbitrary. He's coming at this with a suspicion in mind, and he's almost guaranteed to find some kind of anomalies that would support his suspicion -- no matter what that suspicion. He knows a lot about this Rackstraw guy and that gives him a lot of ways in."

He called Sherwood's conclusions "a textbook example of the Texas sharpshooter fallacy," which is when one ignores information in a dataset that doesn't fit the chosen hypothesis and zeroes in only on "useful" clusters of data until patterns are found that aren't actually there.

Adds Smithline:

"If we are hunting for encrypted messages, this is not the way to go. 'I AM SPONGEBOB SQUAREPANTS' has the same total as 'AND PLEASE TELL THE LACKEY COPS.'"

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Law enforcement scours the area where hijacker D.B. Cooper might have parachuted into in Washington state. (Oregonian file)

Rosulek points to how Sherwood extracted Rackstraw's three military units by finding mirroring combinations of text and numbers that add up to the same amount -- but that to do this required Sherwood to change the rules as he went along.

He notes that with the apparent cipher 7698QA2753, we are meant to add up 7+6+9+8+Q+A+ 2+7+5+3, with Q being 17 and A being 1. But then we are supposed to use the number 11 instead of adding 1 + 1.

Here is Sherwood's decoding work on that cipher, which surfaced the 11th General Support Company, one of Rackstraw's military units:



7698QA2753: 47+Q/17+A/1 = 65; 11th GS = 11+T/20+H/8+G/7+S/19 = 65



"It isn't surprising that he would find [Rackstraw's military units] with his approach," Rosulek says. "And if you keep changing the rules then you are guaranteed to find them -- if you're actively looking for them."

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FBI memo about a "D.B. Cooper" letter

Rosulek says the flexibility Sherwood gives himself allows him to consider "likely millions of different targets for the decoding process... And remember that each of these targets can be 'decoded' in hundreds of different ways." In short: If the process isn't systematic, then it's the Wild West for a codebreaker, leading almost inevitably to the Texas sharpshooter fallacy.

Sherwood stands by his work. The key in finding Rackstraw's units in the ciphers, he argues, is the "slang military terminology" that he says is central to military codes. "You have to understand the reason someone does something," he says. "For Rackstraw, everything for him was military." Sherwood used the number 11 in his code-breaking rather than 1 + 1, he says, because the 11th General Support Company was known as the "Eleventh," not the "One-one."

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Tom Colbert's explanation of Rick Sherwood's decoding work. (Tom Colbert)

Sherwood believes his Army background and Vietnam War experience were essential to his being able to bust the codes, but he does not claim to be a code-breaking genius -- or even necessarily the first person to have broken these D.B. Cooper ciphers. "It's a good possibility" that the FBI cracked the codes long ago, he says.

One theory that Colbert, Sherwood and others have considered is that the FBI dropped Rackstraw as a suspect in the late 1970s not because they didn't believe he was the skyjacker but because he was working for the CIA.

"Nobody broke this code for 47 years?" Sherwood says. "Why not? Why isn't the FBI going after him?"

-- Douglas Perry

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Oregonian file

More D.B. Cooper adventures

-- The D.B. Cooper suspects everyone should know

-- Ultimate D.B. Cooper hunter wanted adventure, not outlaw's capture

-- New D.B. Cooper sleuth challenges long-held beliefs about skyjacker

-- D.B. Cooper letter offers coded clue that might reveal skyjacker

-- D.B. Cooper team accuses FBI of cover-up, 'flat-out lying'

-- D.B. Cooper case offers up another surprising suspect, Walter Reca

-- Skyjacker's real identity revealed, code-breaker claims

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