Hong Kong¡¯s High Court is set to start on Thursday the landmark national security trial of three former leaders of a now disbanded group that organized annual vigils marking Beijing¡¯s 1989 Tiananmen Square crackdown on pro-democracy protesters.

Once legal in China-ruled Hong Kong, such public commemorations ?were hailed as a symbol of the city¡¯s relative freedom compared to mainland China.

The events on June ?4, ?1989, when Chinese troops opened fire to end the student-led protests, are not publicly ?discussed in China, which treats the date as taboo and allows no public remembrance.