After collecting eyewitness testimonies and analyzing the likely weapons systems that were used to facilitate a chemical-weapons attack that targeted rebel-controlled suburbs in Damascus last month, Human Rights Watch (HRW) said Tuesday it believes it has enough evidence to prove that the Syrian government was responsible for the atrocity.

HRW’s extensive investigation, which relied on expert analysis from chemical-weapons and arms specialists along with witnesses’ accounts, concluded that the surface-to-surface rocket systems used to carry out the attack, along with the large quantity of nerve agent that was deployed during the assault on Aug. 21, match up with equipment that is only possessed by government troops in Syria.