A couple of things that I remember from this massacre. Elements of the so called "peoples army" were called in from remote provinces to crush the protest. They didn't know what they were crushing. As they fired into the unarmed crowd, sections of the crowd responded by singing The Internationale, the communist anthem. Notice that many of the protesters are carrying red flags. Mao warned that this sort of thing could happen before he died in 1976, if his supporters (the "Gang of Four") were defeated. I can dig up the quotes.
It's good to point out how ruthlessly the Chinese government is still editing this massacre. Nevertheless, our western press also edits our memory of what really happened, albeit more subtly.
It wouldn't do to be too critical of a government on which we now apparently depend for saving capitalist economies from total collapse.