A pro-democracy demonstrator burns a letter next to pictures of missing staff members of a publishing house and a bookstore during a protest to call for an investigation behind their disappearance, outside the Chinese liaison office in Hong Kong

A pro-democracy demonstrator burns a letter next to pictures of missing staff members of a publishing house and a bookstore, including Gui Minhai, a China-born Swedish national who is the owner of Mighty Current, Cheung Jiping, the business manager of the publishing house and Causeway Bay Books shareholder Lee Bo (L-R), during a protest to call for an investigation behind their disappearance, outside the Chinese liaison office in Hong Kong, China January 3, 2016. Hong Kong opposition lawmakers protested on Sunday outside Beijing's representative office in the Chinese-ruled city over the disappearance of a bookseller who specializes in publications critical of the Communist Party government. REUTERS/Tyrone Siu