Speculation that Amelia Earhart was imprisoned by the Japanese has intensified after a man with ties to the island of Saipan recalled an anecdote that supports the claim.

Aviation pioneer and American heroine Earhart went missing in July 1937 while attempting to circumnavigate the globe in an aircraft.

A number of alternative theories compete to explain what happened to her and co-pilot Fred Noonan, who were never seen again.

One of them purports that the pair landed on islands within the Japanese South Pacific Mandate and taken captive by Japanese troops.

This explanation was elaborated on in a book written by CBS correspondent Fred Groener in the 1960s.

Now a man with family ties to the tiny Pacific island of Saipan has come forward with an explosive tale passed down from his uncle.

William "Bill" Sablan was born in Guam, a US territory, to a Guamanian mother and a father from Saipan.

He told USA Today that on a trip to Saipan in the 1970s he mentioned to an uncle that he had always dreamed of being a pilot.

As soon as he had uttered the words, his uncle gave him "a funny look" and then recalled the explosive story.

According to Sablan, he said: "You know there was an incident here in Saipan back in the middle of the 1930s... an American woman and an American gentleman were brought in by the Japanese for questioning. They were found in some farther southern islands and brought to Saipan because Imperial Japan was notified about them.

"But Imperial Japan didn't want anything to do with them because they didn't want to be involved in any national scandal so I think they were both killed in Saipan and buried there."

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Sablan's fascinating tale will be grist-to-the-mill for the growing online community of Amelia Earhart conspiracy theorists searching for alternative and exotic explanations to her disappearance.

The History Channel documentary featured a photograph of a Caucasian man and woman on the nearby Marshall Islands, which it claimed could have been Earhart and Noonan.