Israel and the US had joined forces, initially in secret, to monitor all of the suspected CW storage depots scattered through Syria; there were more than 20 of them. Any effort to begin preparing for a CW warfare attack would immediately trigger alarms in the US and Israel, and the government in Tel Aviv would begin preparing for a pre-emptive air force attack. The joint US-Israeli system did not signal an alarm in the hours before or after the CW attack near Damascus — clear evidence that the attack could not have come from a Syrian CW facility. To this date, despite constant references by the media to the Syrian attack, there has been no specific evidence linking the Syrian version of sarin, whose sophisticated additives and chemical make-up is known to the West, to the far cruder sarin found at the site.