Lyle Christiansen was watching "Unsolved Mysteries" one night at his home in Morris, Minn., a few years back. It was a show about the legendary D.B. Cooper, who hijacked a Northwest Airlines flight in November 1971 and jumped out of the plane with $200,000 in ransom.

He was never found.

"That's my brother Kenny," Christiansen said to himself.

Since then, Christiansen has led a quixotic crusade to convince the FBI that Cooper was his brother, now dead. Like hundreds of others who have contacted the FBI at some point, Christiansen belongs to a cult of people who believe they know who committed, as the lead FBI investigator calls it, "the country's greatest mystery."

Christiansen's claim is a subject of a long feature in the most recent New York magazine. As the story spread to Washington state, it got residents in Kenny's hometown excited about the tourism potential -- and former neighbors riled about the accusation.

While some involved with the case think Christiansen is onto something, the agent now leading the Cooper case isn't buying it.

"I'm sure he absolutely believes his brother is D.B. Cooper," said Larry Carr, who has been the lead investigator on the case for just over a year. "It is surprising how aggressive people get, once they latch onto their suspect and say, 'Hey, he's our guy.' No matter what you tell them, they refuse to believe you."He's not a viable suspect," FBI spokeswoman Robbie Burroughs said.

Thirty-six years after Cooper disappeared into the night, America is still fascinated by the case. There are scores of websites, books, movies and songs. The country's only unsolved hijacking has become an iconic back story for everyone who has dreamed of getting away with something or getting away from everything.

"In my case, the fascination is with an unsolved crime that's stuck in my memory for all these years," said Bill Crider, an author who also has an online pop culture magazine. "I'm a mystery writer, so I like solutions."

Carr, who worked as a Sauk Rapids, Minn., police officer before joining the FBI, laughs when asked if he did something wrong to inherit the Cooper case.

"I asked for it," he said. "I'm fascinated with it."

Carr said the FBI gets "hundreds and hundreds of stories. It's slowed down over the years, but we still get one every month."

Some day, he thinks, advances in technology could help him crack the case.

Carr also said recently that he plans to reinvigorate the case by releasing details never before seen by the public -- including notes written by the flight attendants and conversations between the plane and the tower -- in hopes that will prompt new clues.

How the legend was born

It was Thanksgiving Eve in 1971. A man who gave the name Dan Cooper bought a ticket for a Northwest Orient Airlines flight from Portland, Ore., to Seattle.

Shortly after the plane took off, the man handed the flight attendant a note, saying he had a bomb. He wanted $200,000 in cash and two parachutes when he landed in Seattle.

The money was brought aboard the plane, which took off for Mexico. Over southern Washington, the hijacker jumped out the back door of the plane into the freezing rain -- and was never seen again.

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.'"

Gray also found Ralph Himmelsbach, the FBI's lead agent on the case before Carr. He concurred that Christiansen was too short and had the wrong color of eyes, but declared him a "good suspect."

But Carr remains skeptical. "The other thing I find strange is that he'd be bold enough to hijack a plane from his own company," Carr said. "Someone would have recognized him."

Regardless, Lyle Christiansen's tale will be added to the FBI vault in Seattle, where the D.B. Cooper legend grows under a sign that reads: "Do not destroy. Historical value. National Archives."

Jon Tevlin • 612-673-1702

Jon Tevlin •