A man who some believed to be the elusive D.B. Cooper died Tuesday in Southern California.

Robert Rackstraw, who was featured in a 2016 History Channel documentary about the notorious criminal, was pronounced dead at home in the early hours of July 9, according to the San Diego Medical Examiner’s Office. He died of a “long-standing heart condition,” according to the San Diego Union-Tribune.

Cooper, known for the hijacking of a flight bound for Seattle from Portland, Ore., is thought to have leaped from the plane with $200,000 in cash. Authorities tracked down hundreds of potential suspects but were never able to find Cooper or his body.

The hijacking, the longest unsolved crime of its kind in FBI history, has baffled official and unofficial investigators for decades. Though the FBI closed the case in 2016, theories about the identity of Cooper have continued to swirl.

In the late 1970s, the FBI briefly investigated Rackstraw in possible connection with the case, according to the Union-Tribune, but later dismissed him as a suspect because he was too young at the time to fit the description of Cooper.

The Washington Post’s Ian Shapira previously reported that the FBI “wouldn’t confirm or deny that Rackstraw had been one” of the 1,000 suspects looked at.

A man wearing a suit, black tie and white shirt approached the counter of Northwest Orient Airlines in Portland and paid for a one-way ticket to Seattle. It was Nov. 24, 1971, and he said his name was Dan Cooper, according to a report by the FBI.

Once on the plane, the man ordered a bourbon and a 7-Up and then handed a note to a flight attendant. The note stated that he had a bomb in his briefcase. He then opened it somewhat to reveal red sticks and wires.

“Soon, she was walking a new note to the captain of the plane that demanded four parachutes and $200,000 in twenty-dollar bills,” according to the FBI statement.

Cooper allowed the flight to land in Seattle and the 36 passengers to deplane in exchange for the cash. He then instructed the pilot to begin a flight to Mexico City.

But Cooper would never land with the plane. He is believed to have jumped from the plane somewhere between Seattle and Reno, Nev.

Thus began the mysterious tale of D.B. Cooper, a name coined through a miscommunication by the media at the time.

Rackstraw is certainly not the only person to fall under the public gaze of speculation surrounding the high-profile hijacking. Many others have been theorized to be the one who stole the cash. The FBI did not rule out the possibility that Cooper might have died after the jump.

As previously reported by The Post’s Shapira, Rackstraw did not reveal whether he was Cooper. He worked at a boat shop and once taught a law course in 1999 at the University of California Riverside Extension.

Rackstraw, a former Army helicopter pilot who had been awarded a Silver Star for valor, didn’t surface as a suspect until the late 1970s, according to news reports. He’d been arrested on charges of murdering his stepfather, but was acquitted in a trial in 1978.

The following year, he faced charges of aircraft theft, possession of explosives and check fraud, according to news reports. Colbert said Rackstraw was convicted and spent more than a year in jail before being released in 1980. Rackstraw’s attorney said he couldn’t confirm those details. Asked by The Post how the charges were resolved, Rackstraw said, “I was acquitted of everything as I recall.”

Geoffrey Gray, the author of “Skyjack,” the most authoritative history of the Cooper investigation, said Rackstraw was never a serious suspect; he is not mentioned once in Gray’s book.

Ian Shapira. Washington Post

In 2011, Thomas J. Colbert, a Los Angeles-based television and film producer, organized a 40-member team to investigate Rackstraw and figure out whether he may have been Cooper. Colbert and his attorney, Mark Zaid, spoke with Rackstraw and asked him to be part of a book or movie about the D.B. Cooper mystery.

In July 2016, a History Channel documentary detailed Colbert’s quest to figure out whether Rackstraw was the notorious hijacker.

“While my cold-case team believed he was Cooper,” Colbert said, “he was also a husband, father, grandfather and great-grandfather.” He said he sends condolences to Rackstraw’s family.

Zaid said Rackstraw “would always sort of go up to the line and sometimes cross it as far as admitting he was D.B. Cooper and then he would just joke about it.”

Zaid said he reached out to both the Justice Department and the FBI to notify them of Rackstraw’s death. He said he asked that they process and release “all Rackstraw-related documents in the D.B. Cooper investigative file.”

Rackstraw previously told The Post he was a “homeless, disabled veteran.” He also said at the time that he was working on a book and a movie about his life.

“Watch the movie,” he said, before adding: “It’s been asked for 45 years. I was never charged. I was made a victim and suspect and holy hell was raised throughout my life.”

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