This report clearly indicates that the Russians along with Assad carried out a chemical attack:
https://en.wikipedia.org/wiki/UN_investigation_of_chemical_weapons_use_in_Ghouta

How about this one, which indicates it was Assad:
https://obamawhitehouse.archives.gov/the-press-office/2013/08/30/government-assessment-syrian-government-s-use-chemical-weapons-august-21

CNN is now reporting that survivors of the latest Assad atrocity are saying bombs fell from planes:
http://www.cnn.com/2017/04/05/middleeast/idlib-syria-attack/