Not a reactor - something far more vicious - Haaretz - Israel News

http://www.haaretz.com/hasen/spages/926815.html

"In my estimation this was something very nasty and vicious, and even more dangerous than a reactor," says Even. "I have no information, only an assessment, but I suspect that it was a plant for processing plutonium, namely a factory for assembling the bomb." 

In other words, Syria already had several kilograms of plutonium, and it was involved in building a bomb factory (the assembling of one bomb requires about four kilograms of fissionable material). 

Processing the plutonium and assembling the bomb require utmost caution, because plutonium is one of the most toxic and radioactive materials. One microgram can kill one person, and a gram is capable of killing a million people. Handling it requires special lathes, but because of its lethal nature nobody is allowed to come into direct contact with plutonium or with the lathes. That is why there is a need to build labs containing dozens of glove boxes, which isolate and separate the worker from the material and the equipment. 

What reinforces Even's suspicion that the structure attacked in Syria was in fact a bomb assembly plant is the fact that the satellite photos taken after the bombing clearly show that the Syrians made an effort to bury the entire site under piles of earth. "They did so because of the lethal nature of the material that was in the structure, and that can be plutonium," he said. That may also be the reason they refused to allow IAEA inspectors to visit the site and take samples of the earth, which would give away their secret.