As we do not know why the Israelis decided to bomb this empty building according to the Syrian President. Then you cannot make any statements about what was inside this empty building. You can only comment on the fact that the Israelis mounted a military raid on a soveriegn state. If it was a nuclear facility and the US and Israelis had proof of this I personally do not think the US would have handed over $25 million worth of fuel to North Korea yesterday. The reason the Israelis are not shouting why they did this is because they worked under the idea there might be something there rather than there is something there. Therefore I believe President Assad when he says that it was an empty building.
Second rocket fired from Gaza explodes inside Strip (Haaretz)
from the article: IDF lifts censorship of Sept. 6 IAF strike on target inside Syria