Video shows what may have triggered Tibetan rioting...
Protest 1988 Documentary
Archive: Chinese troops fire on protesters in Tiananmen Square - BBC News
The 1987–1989 Tibetan unrest were a series of pro-independence protests that took place between September 1987 and March 1989 in the Tibetan areas in the People's Republic of China: Sichuan, Tibet Autonomous Region and Qinghai, and the Tibetan prefectures in Yunnan and Gansu. The largest demonstrations began on March 5, 1989 in the Tibetan capital of Lhasa, when a group of monks, nuns, and laypeople took to the streets as the 30th anniversary of the 1959 Tibetan uprising approached. Police and security officers attempted to put down the protests, but as tensions escalated an even greater crowd of protesters amassed. After three days of violence, martial law was declared on March 8, 1989, and foreign journalists and tourists were expelled from Tibet on March 10. Reports of deaths and military force being used against protesters were prominent. Numbers of the dead are unknown.