@Setanta,
I clearly remember that initially there were reports that the students and the military had peaceful interactions, and I recall thinking that perhaps this uprising had legs if the PLA wasn't prepared to fire on the Chinese people. I also recall reports that the central government was bringing in troops from outside the city because it was concerned that those stationed in and close to Beijing might not follow orders to fire on the protesters. In fact, I believe I also recall reports of clashes between the troops brought into Beijing under the command of a hard-line general and local units.
I did some quick searching and found these photos.
http://www.latimes.com/news/nationworld/nation/la-fg-tiananmen-pictures,0,2772612.photogallery
May 19, 1989
Beijing police parade through Tiananmen Square carrying banners in support of striking university students. The students were in the sixth day of a hunger strike for political reform.
May 21, 1989
An unidentified student demonstrator offers food to People’s Liberation Army troops in Feng Tai near Beijing. The troops’ convoy had been stopped by roadblocks as they were enroute to the Chinese capital.
June 2, 1989
A woman soldier sings among pro-democracy protesters occupying Tiananmen Square. Police officers and troops would occasionally mix with protesters in an effort to keep the demonstration peaceful. In the early morning hours of June 4, 1989, soldiers overran the square, leaving hundreds dead.
Either my memory is very faulty or there is more evidence to be found. I'll keep looking.