It is the Tibetans who first conducted violence. The protesters were targeting shops and vehicles owned by the Han Chinese and set fire. Innocent civilians have been beaten and killed by these people. Read this: http://en.wikipedia.org/wiki/2008_unrest_in_Tibet

The protesters in Lhasa attacked police before rioting, and the ease they bypassed the police with shows they were well organized.

Even if the enemy shoots, the Chinese police cannot shoot back without permission. In any cities if there are riots of such scale, there will be gunshots.