A massive police presence around China's Tiananmen Square marked the 20th anniversary Thursday of the bloody anti-communist protests.

Plain clothes police officers blocked foreign journalist from getting into the square to report on the anniversary.

Security personal blocked TV cameras and prevented still photographers from filming.

The government also shut down social networking sites like Twitter and Flickr, as well as blacked out CNN's coverage of the event.

The government has a history of keeping quiet about Tiananmen Square.

And when young Chinese are asked about it -- they know very little.

CBN News asked one student on the street, "What about you do you know what happened? 

"No, sorry, I don't know," came the reply.

During the 1989 Tiananmen Square protest, the Chinese military killed thousands of student activists.

The Chinese government to this day has never allowed any independent investigations into the incident.
 
Bob Fu remembers well those days in 1989 -- he was a student leader in the Tiananmen protests.

Today, he lives in the U.S. and is president of the China Aid Association, a Christian group that speaks up for human rights and religious freedom in China.

CBN News Senior Reporter George Thomas interviewed Fu about the aftermath of the Tiananmen uprising and what it meant for China. Click the player watch.