Story highlights Publisher Lee Bo is the fifth person linked to Hong Kong bookseller Mighty Currents reported to have gone missing

Hong Kong police announced Lee's missing person report was canceled upon the request of his wife

The mysterious disappearances haven't stopped Hong Kong's forbidden books industry

Hong Kong (CNN) A government investigation into the mysterious disappearance of five Hong Kong publishers and book sellers this week thrust an unusual publishing industry into the media spotlight.

In this free-wheeling, specially-administered corner of China, several publishing houses and bookshops have spent years churning out books banned on the Chinese mainland.

Speciality bookseller Paul Tang says the books focus on taboo topics: politics, religion and sex. "All forbidden in China," he adds.

Tang spoke to CNN within the tight confines of the People's Bookstore, his book-lined shop and coffee-house perched overlooking Hong Kong's high octane Causeway Bay commercial district.

Cheekily-decorated with vintage posters of Chairman Mao, the shop caters to customers who come almost exclusively from the other side of the northern, "internal" border which divides this coastal city from the rest of China. As for the titles he sells, "50% of our books are not allowed in China."

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