Less than two weeks from a massive celebration of China’s 60th anniversary as a Communist state, Beijing is flooded with policemen and the city is on the highest state of security alert permissible outside wartime.

But that did not stop a man going beserk with a knife yesterday evening not far from Tiananmen Square, where a huge military parade is planned for Oct. 1. He killed two people and injured 14.

So much for the massive security presence. But what is equally striking is that the public has been told practically nothing about the dramatic incident.

The state news agency Xinhua issued a terse report Thursday evening giving the man’s name, home town, and the number of his victims. On Friday it released another brief article saying he had been drunk when he went on the rampage.

No newspaper website was allowed to print anything more. Blogs and Twitter posts discussing the stabbings and adding supposed details of what happened were censored almost as soon as they went up. (The Hong Kong-based South China Morning Post, for example, reported that three men were wielding knives and that two escaped.)

Perhaps the authorities were embarrassed that something so dreadful could happen a few hundred yards from Tiananmen Square at a time when it was blanketed with policemen guarding preparations for a parade rehearsal due to be held throughout Friday night.

Perhaps the perpetrator had just lost his job, or suffered some other indignity that would not promote the image of harmony and peace that the government is so keen to present at the anniversary.

But perhaps, too, the massive and sudden censorship reveals something about the Chinese leadership’s idea of security – and of reality. They can’t keep people safe from an attack like this (nor can any government) but they can stop people talking about it, and it is the talking that really makes them nervous.

It is as if they think that if nobody knows what happened, it didn’t happen. But even if nobody hears a tree falling in the forest, that does not mean that it did not fall.