It is kind of interesting from a historical perspective that the massacre part of Tiananmen Square didn't happen in the Square. Like most police actions from fascist states, it was squads of pigs chasing down protesters after they broke and ran and beating them to death or disappearing them when they're cut off from support.
And, of course, the crowd had to break and run. They weren't armed, and couldn't actually resist riot cops, much less the army.