What was behind the Israeli raid on Syria?

One of the more intriguing events of recent weeks has been the Israeli air raid on Syria earlier this month. Why the Israelis felt obliged to act remains clouded in secrecy but one of the theories doing the rounds is that the Israelis were trying to knock out a nascent Syrian nuclear programme. Bret Stephens, a former editor of the Jerusalem post, takes up the story in the Wall Street Journal:

What's beyond question is that something big went down on Sept. 6. Israeli sources had been telling me for months that their air force was intensively war-gaming attack scenarios against Syria; I assumed this was in anticipation of a second round of fighting with Hezbollah. On the morning of the raid, Israeli combat brigades in the northern Golan Heights went on high alert, reinforced by elite Maglan commando units. Most telling has been Israel's blanket censorship of the story--unprecedented in the experience of even the most veteran Israeli reporters--which has also been extended to its ordinarily hypertalkative politicians. In a country of open secrets, this is, for once, a closed one. 
...
The only people that can provide real answers are in Jerusalem and Damascus, and for the most part they are preserving an abnormal silence. In the Middle East, that only happens when the interests of prudence and the demands of shame happen to coincide. Could we have just lived through a partial reprise of the 1981 Israeli attack on Iraq's Osirak nuclear reactor? On current evidence, it is the least unlikely possibility.