When people turn out to mourn the loss of loved ones, local authorities in most places treat them with respect. Not in the northwestern Chinese city of Urumqi last week, where 39 people were killed in a terrorist attack the government attributed to Uighers, a mostly Muslim ethnic minority.

After mourners left chrysanthemums by a charred tree where an explosive went off, riot police picked up the flowers and tossed them in dumpsters. Later that night, when hundreds more came to the site where the attackers had crashed SUVs into shoppers, police tried to block people from lighting candles and pushed them back with riot shields.

"I'm very disappointed, very disappointed," said Robert Wang, 27, whose father was injured in one of the explosions. "I think we should at least have such a right to mourn the dead because we are very sad victims."

Why the heavy hand?

Chinese authorities see crowds and memorials as potentially dangerous . For instance, China's Internet censors permit criticism of the government, but blunt any attempts at collective action that could threaten it.

It was the death of Hu Yaobang, who favored reform, that sent thousands of students into Beijing's Tiananmen Square 25 years ago and sparked the demonstrations that threatened the regime.

In Urumqi, messages had circulated on WeChat, a popular social media app, calling for an evening protest.

Authorities were worried a protest could morph into public criticism of the local government for failing to stop two suicide attacks in the city in less than a month. They also wanted to avoid a repeat of 2009, when demonstrations devolved into a race riot between Uighers and ethnic Han Chinese that left about 200 people dead.

To ensure none of this happened, officials called in People's Armed Police personnel in camouflage carrying automatic rifles with shiny bayonets.

Yet not a single public official actually showed up at the vigil.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.