The name was fake. Some of the money was found years later in the mountains.
The legend of D.B. Cooper was born.
Some think Cooper was killed in the fall. Various other criminals have been suspects or claimed credit, but the case remains open.
In a recent interview, Christiansen said he was struck by his brother's resemblance to a sketch of Cooper. Kenny was also a paratrooper and a Northwest flight attendant.
Shortly after the hijacking, Kenny bought some land in Washington with cash and liked to treat his friends, even though he continued to scrape by on his airline salary.
On his deathbed in 1994, Kenny told Lyle he had a secret. But, he added, "I can't tell you."I said I didn't want to know anything bad about him," Lyle recalled. "I said, 'We love you, anyway.'"
A vault filled with stories
Carr said a vault at the FBI headquarters in Seattle is filled with stories like Christiansen's. Most contain enough details to be somewhat plausible.
Christiansen's story is emblematic of a seemingly unbridled public hunger for mystery and adventure, and a desire to be part of something unknown and legendary, Carr said. "Everybody loves a good mystery."
But after reading the New York magazine story, Carr doesn't think Kenny Christiansen is D.B. Cooper.
"He had brown eyes. He was too short," Carr said. "The stewardess who spent the most time with Cooper said he had hazel eyes and that she looked up to him, and she was 5 foot 8. I'm not going to say it's not him, but I probably won't put a lot of effort into an investigation."
Carr did not interview Lyle Christiansen, 77, a retired post office worker, but FBI agents in Minnesota did, Christiansen said. They never called him back.
So Christiansen tried to get his story to writer Nora Ephron, who wrote the movie "Sleepless in Seattle," which Christiansen liked. When that failed, he paid private investigators in New York City to hand-deliver his message.
Ephron never called him.
But Skipp Porteous, owner of Sherlock Investigations in New York, was captivated by Christiansen and began a correspondence. Porteous eventually began to believe the Minnesotan was onto something.
Finally, he got the story to a writer for New York magazine.
"I believe Lyle, but I'm not surprised that the local FBI doesn't believe him," Porteous said. "I think Kenny Christiansen is the closest we have come to D.B. Cooper."
Geoffrey Gray, the author of the story, tracked down Florence Schaffner, the flight attendant who saw Cooper's "bomb" in a briefcase. She said it was the closest resemblance of Cooper she had seen, "But I can't say, 'Yeah.'"