US Sends Letter On Syria to UN

From AP 

Here is what you need to know 

• U.S. Ambassador Susan Rice detailed the attacks in a letter to U.N. Secretary-General Ban Ki-moon

• It said sarin was used in a March 19 attack on the Aleppo

• updated U.S. intelligence assessment concluded "that the Syrian government has used chemical weapons on a small scale against the opposition multiple times in the past year."