inspectors who were there can take blood and hair samples, brain tissue samples from deceased victims and run them through a device called a gas chromatography machine. even if that area of damascus was decimated by syrian army shelling right after the chemical attack, experts say it's not degraded to the point where you can't get an accurate test. they can grab samples from walls. they may not be prevented from getting an accurate sample. >> appreciate your reporting. secretary of state john kerry making the case for action abroad. cnn's elyse labott traveling with him.