In terms of the source, on a side note, I personally know people who were on the square that day, and later escaped to the US to seek asylum under Chinese Student Protection Act of 1992 [1]. They have a lot of first-hand information and photographs, but wouldn't release them to media because they still have families live in China, and as a consequence of release those information, PRC may reject their entry in the future. To most of the people getting the truth out to the world doesn't outweigh the freedom of visiting families and friends, which is reasonable.

[1] https://en.wikipedia.org/wiki/Chinese_Student_Protection_Act...