An Indiana Army vet says he used his code-breaking skills to crack a nearly 47-year-old mystery—the identity of the infamous airline hijacker D.B. Cooper.

Cooper became a folklore legend after parachuting from a jet in 1971 in a business suit and escaping with $200,000 in ransom money. The FBI closed the case two years ago without identifying a suspect and after recovering only a portion of the stolen loot.

The Indiana Army vet who believes he solved the mystery is Rick Sherwood, 70, of Wheatfield. He believes the hijacker is a former military pilot named Robert Rackstraw, The Indianapolis Star reported Friday.

Sherwood worked with codes during the Vietnam War. As a result, he used that knowledge to decipher two letters reportedly written by Cooper in 1971 and 1972.

One of the letters contained an incongruous string of numbers: “717171684*”

“The numbers just didn’t belong,” he told the paper.

The letter began tauntingly, “I knew from the start that I wouldn’t be caught,” and was sent to four papers: The Washington Post, The New York Times, The Los Angeles Times and The Seattle Times.

Eventually, Sherwood took “717171” to mean the 371st, the unit he and Rackstraw had been assigned to briefly in Vietnam. He said they never met but could have communicated on the radio during missions.

“When the 371st come up, I seen that, I’m going: ‘Yes, this is it. This is the beginning of breaking that code,’” he told the paper.

Using a simple letter counting system, he found other clues that pointed to Rackstraw, according to the news organization.

With the second letter, Sherwood decoded secret messages by keying in on repeated words and phrases, The IndyStar reported.

He told the paper that a line that says “and please tell the lackey cops, D.B. Cooper is not my real name,” hides the coded message, “I am 1st Lt. Robert Rackstraw.”

Nevertheless, the paper reported that Sherwood admitted he could be wrong since he was finding what he wanted because he was working from the assumption the letters were from Rackstraw. But he thinks there is just too much for it to be a coincidence or wishful thinking.

The FBI turned over both letters to documentary filmmaker Thomas Colbert as part of a lawsuit seeking access to the voluminous Cooper investigative file.

Colbert affirmed Sherwood’s opinion. He said in a book that Rackstraw was Cooper. He also leads of team of amateur Cooper sleuths with experience in law enforcement and the military that has been pursing Rackstraw for years.

The FBI says it will reopen the D.B. Cooper case only if it obtains Cooper’s parachute or more of the ransom money.

Fox News has reported that Rackstraw denied he was Cooper in rambling letters he sent to the judge hearing Colbert’s lawsuit last year. At the time he was 73 and living in San Diego.

The FBI cleared Rackstraw as a Cooper suspect in the 1980s, according to The IndyStar, which reported that during a brief interview Rackstraw refused to directly deny he was the legendary outlaw.

“Don’t get down to the bottom line,” he said. “That’s a 40 million dollar question for Christ’s sake.”

He also told the paper Colbert’s claims were “fake news.”