Now, 40 years later, comes what seems like a tantalizing new tip. The Federal Bureau of Investigation says it has a new suspect, one whose name has never surfaced in the ocean of tips that has washed in over four decades.

Fred Gutt, a special agent in the Seattle office of the F.B.I., told The New York Times on Monday that the suspect died 10 years ago. He said the tip came from a retired law enforcement officer who knew a witness who “had an association with” the suspect from long ago.

“After the suspect died, the witness was more comfortable sharing some secrets, if you will,” Mr. Gutt said. The tip, first reported by The Telegraph, the British newspaper, was deemed credible because it came from someone in law enforcement.

The new reports set off another round of speculation and conspiracy theories across the Internet. And the news media again besieged the tiny town of Ariel in southwest Washington, near where Mr. Cooper is believed to have landed. There, in so-called Cooper Country, the Ariel Store and tavern, an archive of Coopermania, has kept the story alive with an annual get-together that toasts Mr. Cooper as a hero.