Tiananmen, a Chinese taboo

It's the most taboo subject in modern Chinese history; a trauma for an entire generation of students, intellectuals and democrats who protested for seven weeks in the spring of 1989, demanding an end to corruption and a start to political reforms. Today, 30 years after the Tiananmen Square massacre, in which thousands of students were killed by the army in the heart of Beijing, the Chinese authorities continue to deny the facts and prevent any commemorations. Our correspondents report.