It was pretty clear that the official Chinese number of 200 civilian victims was too low, but 10,000?

via Wikipedia

Tiananmen Square protest death toll 'was 10,000'

"The Chinese army crackdown on the 1989 Tiananmen Square protests killed at least 10,000 people, according to newly-released UK documents.
The figure was given in a secret diplomatic cable from then British ambassador to China, Alan Donald.
The original source was a friend of a member of China's State Council, the envoy says."

Can't say I would be too surprised if it's really 10,000, but even though the source was near the center of power, this does not necessarily mean that the number is actually accurate. What we can say, though, is that the number of victims was probably somewhere in the range of 1,000 to 10,000.
Doesn't make much of a difference, anyway. It was mass murder.