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.