Nearly 40 years after Cooper parachuted into the cold night air from a hijacked Northwest Airlines flight with $200,000 in cash strapped to him, the mystery man is still being pursued not only by law enforcement but also by an informal network of hobbyists and armchair sleuths.
Many of the self-deputized investigators have spent years if not decades searching for the man who on November 24, 1971, boarded a flight from Portland, Oregon, to Seattle, coolly told a stewardess he was carrying a bomb and wanted money.
When the plane landed in Seattle, he received the money and parachutes, let the passengers go and instructed the pilot to fly to Mexico City at low altitude. It is believed that he jumped somewhere over Washington state.
"It's a chance to be a part of this case, part of history. It's not the JFK assassination but it's up there," said Tom Kaye, who retired from his job running paintball manufacturing businesses to become what he describes as a "gentleman scientist."
His retirement plans, though, shifted from looking for dinosaurs to tracking Cooper's fading tracks.
Kaye is part of a small team of amateur investigators, including a scientific illustrator and metallurgist, that for three years has analyzed elements of the case evidence like the tie found on the hijacked plane that could have belonged to Cooper and some of the cash that he took, which was later recovered.
The team has been granted access to the evidence file since, Kaye said, "We have the time and the resources. The FBI has plenty of other crimes to solve."
A spokesman for the FBI's Seattle Field Office, Fred Gutt, said while the FBI understands there is great public interest in this long-unsolved case, "it's a fairly low-priority case for the FBI" as it pursues new investigations involving cases like missing children that have a current impact on public safety.
During the four decades they have searched for the real Cooper, the FBI has looked at close to 1,000 suspects. Many of them were suggested by people convinced their fathers, brothers or neighbors could have masterminded the only remaining unsolved plane hijacking in U.S. history.
Kaye's team hasn't cracked the case, but he said they believe their long hours have paid off.
"If you believe it's his tie, we have already narrowed the list of suspects," Kaye said. "We look at the particles under powerful microscopes and analyze them. For instance, if there's salt, we can tell the difference between sea salt and salt that came from a shaker. If there's sea salt on his tie that came from the ocean, he didn't pick that up in Illinois."
Kaye said the investigators also traveled to the site where nearly nine years after Cooper's dive from the plane, $5,800 was found on a river bank. The serial numbers on the bills matched some of the cash Cooper took.
Chemical testing of the money was inconclusive, Kaye said. They also floated packets of bills downstream with notes asking for information attached to see how the river might have carried off Cooper's loot. But for all the packets, only one person contacted the team, he said.
Still, Kaye said investigators are hopeful that analysis of the thousands of particles found on the clip-on JC Penny tie Cooper may have left behind on the plane will lead to a break in the case.
"We don't have too little evidence, we have too much," he said.
For Galen Cook, his lifelong interest in the mysterious skyjacker began on his boyhood newspaper route in Alaska.
"There was a big composite drawing of D.B. Cooper on the front page of the local paper, and I took an interest in the case from Day One," he said.
After graduating law school, Cook began peppering the FBI with Freedom of Information Request requests and chasing any lead, no matter how far-fetched.
"I have done it over the years as a hobby, like people build model airplanes or work restoring cars in a garage," he said. "I probably put in a few thousand hours on it."
Cook believes Cooper survived the jump into the night sky, He is at work on a book about his findings, but he doesn't expect his personal investigation to completely close the door on Cooper's mystery.
"There are people out there that tell stories that are so beyond belief I have to walk away," Cook said. "A lot of people look at D.B. Cooper as a great legend and want to be a part of that."
On the Dropzone skydiving website, bloggers have posted thousands of pieces of Cooper trivia and conspiracy.
"DB is alive and well living on the East Coast," one recent posting claimed. "I met him in 2007 and one night after more tequila then the old man can handle he let me in on his secret. He's a cool dude."
Ralph Himmelsbach doesn't see Cooper as toasting his good health and ill-gotten fortune.
Now retired, Himmelsbach was the lead FBI agent on the Cooper case for eight years. He follows developments and speculation in the Cooper case but disagrees with the amateur investigators who think Cooper parachuted away to a better life.
"My feeling has been for a long time is that he didn't succeed," Himmelsbach said. "He's out there somewhere lying in the woods."