This note contained coding that read: 'CAN FBI CATCH ME… SWS', which Colbert said was Rackstraw taunting agents to track him. He added that the SWS stood for Special Warfare School, which is where the veteran supposedly learned coding.
The notorious hijacker, who is one of the 20th century's most compelling masterminds, hijacked a Boeing 727 at Seattle-Tacoma airport in 1971 and held its crew and passengers hostage with a bomb.
Once his demand of $200,000 cash - the equivalent of $1.2 million today - was reached and transferred onto the plane, he had the crew take off before he parachuted out over the dense Pacific Northwest woods and disappeared.
The hijacker was dubbed DB Cooper by the FBI.
The team of sleuths say they have now uncovered secret coding in five different notes supposedly sent by Cooper that ties his identity to Vietnam War veteran Robert W. Rackstraw.
The investigators claim that hidden messages in the coding indicate Rackstraw had a deep covert history with the CIA, which explains why the FBI closed their investigation without finding out the hijacker's true identity.
Tom Colbert, the lead investigator of the 40-person cold case team, revealed his findings outside the J. Edgar Hoover Building in Washington DC on Thursday.
He said the evidence points to a conclusion that the FBI was guilty of 'stonewalling, covering up evidence and flat-out lying for decades'.
Comment: The FBI? Stonewalling? That can't be right. See: The FBI strategy: Stonewall Russiagate until next year's Congressional elections
Colbert had revealed in early January that a code-breaker working for him had noticed a secret coded message in a court-released letter supposedly sent by Cooper.
He said at the time that a nine digit number typed at the bottom of the letter could have only come from Rackstraw because it referred to three covert military units he had ties to during the war.
Colbert revealed on Thursday that his code-breaker had since uncovered the new hidden messages in four other taunting notes sent by Cooper in the late 1970s.
Coding in one note, which was sent on November 30, 1971, said: 'IF CATCH I AM CIA... RWR'.
The investigators believe the 'RWR' in the coding is Rackstraw's initials and that it also indicated that he expected a get-out-of-jail card from the federal spy agency if he was captured.
Another note contained coding that read: 'CAN FBI CATCH ME... SWS', which Colbert said was Rackstraw taunting agents to track him. He added that the SWS stood for Special Warfare School, which is where the veteran supposedly learned coding.
Colbert said two of the letters were mailed within 30 minutes of Rackstraw's old California mountain town.
Coding in this note, which was sent on November 30, 1971, said: 'IF CATCH I AM CIA… RWR'. Investigators believe the 'RWR' in the coding is Rackstraw's initials.
Colbert revealed on Thursday that his code-breaker had uncovered the new hidden messages in four other taunting notes sent by Cooper in the late 1970s, including the one above.
Colbert said the letter mentioned in the article above featured coding that read 'NGJS', which he says stands for his National Guard Jump School training unit.
Colbert revealed in January that a code-breaker working for him had noticed a secret coded message in this letter. He said the nine digit number at the bottom could have only come from Rackstraw because it referred to three covert military units he had ties to during the war.
Investigators questioned Rackstraw about the Cooper case in 1978 and eliminated him as a suspect. When Colbert first publicly named and linked Rackstraw to the hijacking, the veteran's lawyer called the accusations 'the stupidest thing I ever heard'.
Rackstraw had an illustrious military career as a pilot in the 1st Cavalry Division - one of the first major American air assault divisions.
It was there that Rackstraw learned to parachute and was given two Distinguished Flying Crosses for his performance while in the air - but he was kicked out of the army after they discovered he had lied about dropping out of high school and attending two colleges.
Colbert believes the military gave him all the skills he needed to pull off the extraordinary heist.
The FBI revealed in July 2016 that they were closing the investigation, saying that Cooper - whose real identity has never been confirmed by authorities - died of exposure in the woods between Oregon and Washington after jumping from the plane.
A nine-digit number typed at the bottom of a letter, supposedly sent by Cooper, could only have come from one person - a maverick Vietnam veteran Rackstraw.
Colbert said two forensics experts said the handwriting from the letter (right) was so similar to the writing on Cooper's boarding card (left) that it was 'likely' that they 'were written by one person.'
Four of the letters were already known to the public, but Colbert obtained the fifth letter in November in the latest Freedom of Information request he had submitted.
Copies of the typewritten letter were sent to The Seattle Times, The New York Times, The LA Times and The Washington Post by the hijacker at the time.
Colbert argues the letter, which was sent 17 days after the hijacking, proves the existence of an FBI cover-up.
'I knew from the start that I wouldn't be caught,' the letter started, before later saying 'I left no fingerprints.'
The letter wasn't public knowledge beyond a few brief reports in the newspapers that played it off as a prank, according to Colbert.
Colbert said he and his wife hired two forensics experts - one a past president of the American Society of Questioned Document Examiners and the other an ex-FBI agent - to examine the handwritten note.
The two men both said the handwriting was so similar to the writing on Cooper's boarding card that it was 'likely' that they 'were written by one person.'
Colbert said Rackstraw may have included the coded messages in the letters to signal to his co-conspirators that he survived the leap from a Boeing 727 after he hijacked it.
© FBI
© Thomas J. ColbertCopies of the typewritten letter were sent to The Seattle Times, The New York Times, The LA Times and The Washington Post by the hijacker at the time.
Colbert is adamant the FBI was too hasty to wrap up the investigation and now says the revelation of the hidden messages, especially the links to the CIA, proves why the agency has been stonewalling.
He said his team found what they believed to be a parachute strap and foam padding from skydiver's backpack in the forest near Cooper's alleged jump location last year. They turned over the two items, along with the dig site itself, to the FBI.
Colbert believes the FBI still hasn't taken action on any of the team's efforts despite what they provided them.
He has spent several years conducting his own investigation into the mysterious crime, writing a book and producing a documentary series on it in the process.
Colbert said he has extensively investigated Rackstraw as well. In 1977, six years after the hijacking, Rackstraw was suspected of kiting checks for $75,000, but fled before arrest and went to Iran to teach the Shah's men how to fly helicopters.
Meanwhile, back at home, police raided his storage units and found 14 rifles and 150lbs of dynamite. He lost his Iran chopper job and he was brought back the USA, where he was arrested for fraud and the murder of his stepfather. Philip Rackstraw was found in the grounds of his parents' home with two bullets in his head.
Rackstraw was acquitted of murder and made bail on the fraud charge. Then he faked his death, pretending to crash his plane in the ocean at Monterey Bay, California.
He was found and taken in by the FBI, who believed he might be Cooper, but a lack of evidence and the sudden discovery of some of the hijack money in Washington - planted, Colbert says, by an accomplice - led to his release.
Rackstraw made a plea deal and after serving a year in prison for his Stockton convictions, he moved to Riverside, California.
There he taught a law course in mediation before retiring to his yacht, 'Poverty sucks'.
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