Wanted-poster sketch of D.B. Cooper

The infamous skyjacker known as D.B. Cooper revealed his real identity through a hidden message in a letter to The Oregonian in March 1972, just a few months after he parachuted from Northwest Orient Flight 305 and disappeared.

That's the conclusion of a longtime Cooper-case researcher who recently examined the letter with a former Army code-breaker.

For the past couple of years, TV producer Thomas Colbert has been trying to convince the FBI that he and his team of retired law-enforcement and military officers have figured out who Cooper is -- a former paratrooper and Vietnam War veteran named Robert Rackstraw.

Colbert is the author of the 2016 book "The Last Master Outlaw," in which he lays out his evidence against Rackstraw, and producer of the History Channel documentary "D.B. Cooper: Case Closed."

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Robert Rackstraw (Courtesy of Thomas Colbert)

D.B. Cooper, whoever he actually is, became a folk hero after he took over Northwest's Portland-to-Seattle flight on Nov. 24, 1971, secured $200,000 in ransom and then leapt from the plane somewhere over the Northwest. The skyjacker, who bought a seat on Flight 305 using the name "Dan Cooper," has been the subject of songs, books and a Hollywood movie. The case officially remains unsolved.

The popular myth presents D.B. Cooper as a romantic everyman who successfully hit out at The Establishment. But in Colbert's telling, the real Cooper -- Rackstraw -- is a sociopath, a conman and quite possibly a murderer.

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The search for D.B. Cooper (Oregonian file)

So far, the FBI doesn't appear to be taking Colbert's work seriously. The bureau closed the case without resolution in 2016 and has shown no sign of renewed interest in it.

The reason for the FBI giving him the high-hat, Colbert says: The bureau doesn't want to admit that a group of volunteer investigators solved a high-profile case that its G-men couldn't.

"This is obviously about embarrassment and shame," he told The Oregonian in February.

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Oregonian file

Arguably the strongest circumstantial evidence Colbert has are the encrypted codes he says Rackstraw included in letters sent to newspapers in 1971 and '72.

Earlier this year, Colbert revealed that Rick Sherwood, a code breaker during the Vietnam War for the then-covert Army Security Agency and a new member of Colbert's volunteer Cooper cold-case team, had identified an eye-opening code in a Dec. 11, 1971, letter sent to the New York Times, the Los Angeles Times, the Washington Post and the Seattle Times.

Various newspapers received various D.B. Cooper letters in the months and years immediately after the skyjacking. Law enforcement deemed most of them to be hoaxes. But the Dec. 11, 1971, letter excited FBI investigators at the time because it revealed some details about the skyjacking that hadn't been publicly released.

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Flight 305 taking on ransom and parachutes in Seattle (AP)

It also included a series of seemingly random numbers on it. The FBI never made sense of them.

That's because the bureau's agents didn't know what they were looking for, Sherwood told The Oregonian in January. Sherwood, on the other hand, did know what he was looking for: He approached the numbers with Rackstraw as his suspect and with the knowledge that Rackstraw had the same Army "basic cryptology" training he had.

Soon enough, Sherwood found possible ciphers in the numbers that identified Rackstraw's Vietnam military units: the 371st Radio Research Unit, the 11th General Support Company and the Army Security Agency, the same outfit Sherwood also served in.

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Oregonian file

Sherwood admitted it's conceivable that he's simply seeing what he wants to see in the numbers.

"It's not impossible," he said. "But what are the odds that these digits would add up to this? Astronomical. A million to one. Rackstraw didn't think anyone would be able to break it."

Rackstraw, who's retired and living in the San Diego area, was an FBI suspect in the skyjacking until he was "ruled out" in 1979. The former paratrooper made teasing comments to the media in the late '70s hinting that he could be the hijacker, but in recent years he's insisted he is not D.B. Cooper.

(Rackstraw has not responded to phone calls from The Oregonian seeking comment.)

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D.B. Cooper letter with "confession" (Courtesy of Thomas Colbert)

Now Colbert has received another letter via the Freedom of Information Act. This one was sent in March 1972 from Jacksonville, Florida, to The Oregonian, which turned it over to the FBI.

The letter's author states that he's writing from the Bahamas, "so your silly troopers up there can stop looking for me. That is just how dumb this government is. I like your articles about me but you can stop them now. D.B. Cooper is not real."

The writer also offers a motive of sorts for why he pulled off the high-risk crime: "I had to do something with the experience Uncle [Sam] taught me, so here I am, a very rich man."

The letter adds: "And please tell the lackey cops D.B. Cooper is not my real name."

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FBI document (Courtesy of Thomas Colbert)

Sherwood says the rather basic code in the March 1972 dispatch to The Oregonian is all about "converting letters to numbers and back to letters." He noticed the author had repeated key words and phrases in the missive. "I knew that is where the writer had hidden messages," he says. Soon enough, he discovered that the letter-writer, in "code-speak," was identifying himself as "1st LT Robert Rackstraw."

Colbert calls it Rackstraw's "confession."

The D.B. Cooper skyjacking continues to fascinate the public all these years after it occurred -- and suspects continue to surface. In May, a small publisher released a book claiming that a man named Walter Reca was the skyjacker. The evidence offered in support of the late Michigan man being Cooper isn't especially compelling.

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Oregonian file

Colbert's case against Rackstraw is much stronger, but it still has holes. The TV journalist has been accused by some fellow Cooper chasers of fitting facts to his theory and making assumptions.

One example of the latter: Passengers and crew described the skyjacker as middle-aged, but Rackstraw was 28 in November 1971. Colbert says Rackstraw was wearing a toupee and heavy makeup to make himself look older, though he doesn't have solid evidence to back up this assertion.

But with the possible letter ciphers in hand, Colbert is now convinced he not only has unmistakable evidence that Rackstraw is the skyjacker but proof that the former paratrooper has effectively admitted it. Of course, unless Colbert can snare a straightforward confession -- or the FBI gets off the sidelines and offers its own conclusion -- the debate over the D.B. Cooper case is certain to continue.

-- Douglas Perry

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A D.B. Cooper fan (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

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