D.B. Cooper Mystery Man Found Dead!

Suspected 1971 hijacker took secrets to the grave.

Robert W. Rackstraw Sr Wearing Plaid Shirt Next to FBI Drawing Of D.B. Cooper
AMI/Coleman-Rayner; FBI

The former military man suspected of being infamous hijacker D.B. Cooper has died — taking the secret of his true identity to the grave!

Some senior FBI agents thought Robert W. Rackstraw Sr. — a U.S. Army veteran and paratrooper who closely resembled the police sketch of the culprit — was the parachuting thief who in 1971 jumped from a plane over Washington state with $200,000 in ransom money, according to sources.

But it wasn’t until 2016 that Rackstraw was fingered by a team of codebreakers and 40 investigators as the man who pulled off history’s most daring heist!

Now, in a world exclusive, The National ENQUIRER can reveal Rackstraw — who died in his San Diego condominium on July 9 — was known as “Mr. Cooper” at a marina where he’d dock a small yacht.

“Everyone would refer to him as Mr. Cooper. He even had a nickname, Airborne Bob, from some of the guys!” a source snitched.

“He was always boastful that nobody could prove anything!”

PHOTOS: D.B. Cooper — Skyjacker Caught Alive & Well

Though the feds ultimately ruled him out as a suspect, independent investigators said cryptic coding in a 47-year-old letter sent by Cooper to a newspaper proved the hijacker was Rackstraw!

“The fact that code from Rackstraw’s three military units — two of them secret until the late 1980s — were embedded in the letter makes this the smoking gun!” declared filmmaker Thomas Colbert, leader of the sleuths who claimed they unraveled the mystery.

Colbert believes Rackstraw’s dispatch was directed at three co-conspirators who — according to FBI documents and witnesses — helped him escape.

Still, before his death, Rackstraw continued to be evasive.

“They say that I’m him,” he said. “If you want to believe it, believe it.”