Here's the problem:

1) "Rackstraw – a former Special Forces paratrooper, explosives expert and pilot with about 22 different aliases – was once a person of interest in the case, but was eliminated as a suspect by the FBI in 1979. His elimination was controversial amongst the investigating agents, and he remained, for many, the most viable suspect in what remains the only unsolved case of air piracy in the United States."

Rackstraw is the obvious choice.

2) "Rick Sherwood – a former member of the Army Security Agency, which decoded signals during the Vietnam War – cracked the codes. Rackstraw served under Sherwood in two classified units, and Sherwood was familiar with his writing style having deciphered some of his earlier messages."

They got someone who knew Rackstraw to look into whether it might be Rackstraw.

3) "Using codes that only Rackstraw would have known, Sherwood honed in on two sentences for analysis. The first sentence, “I want out of the system and saw a way through good ole Unk,” was decoded to, “I want out of the system and saw a way by skyjacking a jet plane.” And the second sentence, “And please tell the lackey cops D.B. Cooper is not my real name,” was decoded to “I am 1st Lt. Robert Rackstraw, D.B. Cooper is not my real name.”"

This person came up with a possible solution that fingers the exact target he set out to finger.

That's fine as far as it goes, but it'd be a hell of a lot more convincing if either they got a cryptographer with no knowledge of the case or individual to come up with it, or if the target wasn't the obvious guy they were literally looking for evidence against. Especially since the translations, as retold in the article, seem awfully tenuous.

And speaking of those translations! "And please tell your lackey cops" translates to "I am 1st Lt. Robert Rackstraw, "? Really? What sort of code...is this exactly?

I mean, if we assume there's a code where the word "lackey" means "Robert" and the word "cops" means "Rackstraw", and so on, then yes, that sentence does mean what is claimed, but that's 1) a pretty strange code and 2) you could just assume it's a different code where "lackey" means "Vladimir" and "cops" means "Putin", and now it incriminates the Russian president. That there is a code that incriminates Rackstraw doesn't mean it's the code that was used (if, indeed, any code was used; the letters as quoted aren't especially cryptic).

Alternatively...well, what is the alternative? I don't see a lot of potential ciphers here that yield the astonishing results claimed.

> “We now have him saying, ‘I am Cooper,’” Colbert told Seattle PI. “Rackstraw is a narcissistic sociopath who never thought he would be caught. He was trying to prove that he was smarter than anyone else. But he couldn’t fight 1500 years of brainpower on our team.

Maybe they needed a few more years of brainpower. (Also, if you believe the story, it wasn't about 1500 years of brainpower, but the fact that they talked to one guy who used to be Rackstraw's boss, and is claiming without proof that Rackstraw used to use a code where "Unk" mean "hijacking a jet" and "lackey cops" meant "Robert Rackstraw". I don't really believe that, but if you do, then this is mostly just about talking to the one guy who just happened to have the one scrap of secret info that identifies the hijacker, man, if only they'd thought to talk to the prime suspects ex-boss from the very start!

In short: What a pile of nonsense and poor writing.