By Teresa Carson

PORTLAND, Oregon (Reuters) - Journalist David Oliver Relin, co-author of the controversial best-selling book "Three Cups of Tea," took his own life last month in the Columbia River town of Corbett, Oregon, east of Portland, authorities disclosed on Monday.

The cause of Relin's death on November 15 was listed as suicide by blunt force head injury, said Tom Chappelle, Multnomah County deputy medical examiner, but he declined to give further details. Relin, who lived in Portland, was 49.

Relin, a freelance journalist who wrote for several magazines, became best known for his work with Greg Mortenson on the wildly successful memoir "Three Cups of Tea," which was first published in 2006 and spent four years on the New York Times bestseller lists.

The book, which sold over 4 million copies, chronicled Mortenson's failed attempt to climb the mountain K2 in South Asia and his encounter with impoverished Pakistani villagers whom he credited with inspiring him to build schools for young girls and other humanitarian projects in the region.

However, the credibility of the book came under fire in 2011 when the CBS television news program "60 Minutes" aired an expose accusing Mortenson of fabricating or embellishing key details of his story, and using his charitable institute to promote sales of the memoir.

CBS News, for example, disputed Mortenson's account of being kidnapped in Pakistan's Waziristan region in 1996.

Mortenson later acknowledged in an interview posted on his institute's website that the book contains "discrepancies" that resulted from "omissions and compressions" done for the sake of literary expediency. But he insisted the abduction story was "pretty much" true and defended the book overall, saying, "I'm not a journalist. I don't take a lot of notes." Continued...