http://hosted.ap.org/dynamic/stories/M/ML_SYRIA_ATTACK_SCENARIOS?SITE=AP...

The Obama administration, searching for support from a divided Congress and skeptical world leaders, says its own assessment is based mainly on satellite and signals intelligence, including intercepted communications and satellite images indicating that in the three days prior to the attack that the regime was preparing to use poisonous gas.

But multiple requests to view that satellite imagery have been denied, though the administration produced copious amounts of satellite imagery earlier in the war to show the results of the Syrian regime's military onslaught. When asked Friday whether such imagery would be made available showing the Aug. 21 incident, a spokesman referred The Associated Press to a map produced by the White House last week that shows what officials say are the unconfirmed areas that were attacked.

The Obama administration maintains it intercepted communications from a senior Syrian official on the use of chemical weapons, but requests to see that transcript have been denied. So has a request by the AP to see a transcript of communications allegedly ordering Syrian military personnel to prepare for a chemical weapons attack by readying gas masks.

The U.S. administration says its evidence is classified and is only sharing details in closed-door briefings with members of Congress and key allies.

Yet the assessment, also based on accounts by Syrian activists and hundreds of YouTube videos of the attack's aftermath, has confounded many experts who cannot fathom what might have motivated Assad to unleash weapons of mass destruction on his own people - especially while U.N. experts were nearby and at a time when his troops had the upper hand on the ground.

"We can't get our heads around this - why would any commander agree to rocketing a suburb of Damascus with chemical weapons for only a very short-term tactical gain for what is a long-term disaster," said Charles Heyman, a former British military officer who edits The Armed Forces of the U.K., an authoritative bi-annual review of British forces.