In Chinese history, June 4 lives in infamy. On that day in 1989 the Communist Party government sent in tanks to crush protesting students who had raised a Goddess of Democracy on Tiananmen Square. Every year since, the people of Hong Kong have publicly commemorated that terrible day so it is not forgotten.
Beijing found this annoying when Hong Kong was still a British colony. But now that Hong Kong has reverted to Chinese sovereignty, it deems these commemorations intolerable. This explains why three Hong Kong citizens are now on trial, charged with participating in or inciting others to join last year’s June 4 vigil.