[6] The UN report,[3] which was completed on 12 December, found "likely use of chemical weapons in Khan al-Assal" and assessed that organophosphate poisoning was the cause of the "mass intoxication".
“There were signatures in all three of them that matched.”[12] The attack took place in Khan al-Asal, in the context of the Syrian civil war, in the Battle of Aleppo's southwestern front.
Rebel forces had been shelling the village from the surrounding areas for weeks, and had gained control of the police academy located 3 kilometers (1.9 mi) southwest of Khan al-Asal.
[3] A Reuters photographer was quoted as saying that he had visited victims in Aleppo hospitals and that they had breathing problems; he also said that people had told him that the air smelled of chlorine after the attack.
[17] Later on the day, the Syrian government wrote an official letter to the United Nations stating that opposition forces had fired a chemical rocket, "from the Kafr Da'il area towards Khan al-Asal in Aleppo governorate, some 5 km away.
[16] On the day of the attack, an activist from the Syrian Observatory for Human Rights (SOHR) said "16 government soldiers and 10 civilians had been killed after a rocket landed on Khan al-Assal".
[13] A rebel fighter from the Ansar Brigade told Reuters that a missile had hit the town at around 8 a.m., and that he had seen pink-tinged smoke rising after a powerful blast shook the area.
[5] One analyst (Bretton-Gordon) cautioned that conventional high explosives can also produce an odor which might be mistaken for chlorine, and that there was no indication from the images he had seen that the chemical agent had been used.
[24] While Jean Pascal Zanders, a chemical weapons expert and a senior research fellow for the EU Institute for Security Studies, cast doubt on the use of chlorine, saying that one small rocket couldn't deliver the quantity needed to kill 25 people.
White House spokeswoman Caitlin Hayden said on 5 September 2013 that US officials had "studied the Russian report but ... found no reason to change our assessment" that the Syrian government was responsible for the attack.
[8][37] UN/OPCW investigators finally arrived on the ground in Syria on 18 August, after the Syrian government agreed to allow access to two other unspecified sites besides Khan al-Assal, but with a mandate limited to determining whether chemical weapons had been used and if so which ones, but not who had used them.
[9][32] The inspectors' arrival coincided with the much larger-scale 2013 Ghouta attacks which took place on 21 August,[38] pushing the Khan al-Assal investigation "onto the backburner" according to a UN spokesman.
The UN Mission noted that the UN Human Rights Council's Independent International Commission of Inquiry on the Syrian Arab Republic had collected conflicting witness testimony concerning the delivery mechanism for the sarin attack.
Some testimony supported the position that a rocket was fired into the neighborhood, while other witnesses claimed an overflying aircraft had dropped an aerial bomb filled with sarin.
[3] They concluded that the “United Nations Mission collected credible information that corroborates the allegations that chemical weapons were used in Khan Al Asal”.
In an interview published two months after the UN/OPCW findings, Åke Sellström, the chief investigator of the UN/OPCW mission was asked about the possibility that the Khan-al-Assal incident was an opposition chemical attack.
The government was irritated that we didn’t have the mandate to point to the perpetrator at Khan al Asal, that we couldn’t speculate who was the perpetrator.”[39] In June 2013, prior to UN investigators arriving in Syria, the UN's Independent International Commission of Inquiry on the Syrian Arab Republic said that there was reason to believe that "limited quantities of toxic chemicals" had been used in the Khan al-Assal attack, but that it was not then in a position "to determine the precise chemical agents used, their delivery systems or the perpetrator".
[28] On 5 March 2014, the UN Human Rights Council published a report of the "Independent International Commission of Inquiry on the Syrian Arab Republic" (dated 12 February) that stated that the chemical agents used in the attack bore "the same unique hallmarks as those used in Al-Ghouta" in August 2013.
The UN report also indicated, based on "evidence available concerning the nature, quality and quantity of the agents used" that the perpetrators of the Al-Ghouta attack "likely had access to the chemical weapons stockpile of the Syrian military".
[41] Morning (New York): As a response to the Syrian request, Ban Ki-moon decided to conduct a United Nations fact-finding mission to investigate the attack.
[31] Carla Del Ponte, a member of the UNHRC commission of Inquiry told RSI, a Swiss public broadcasting organisation: “Our investigations will have to be further explored, tested and proven through new evidence, but as far as we could determine, at the moment only opponents of the regime have used sarin gas” (roughly translated).
[46][47] The next day, in an apparent reaction to Del Ponte’ comments, the Commission issued a press release clarifying that it “has not reached conclusive findings as to the use of chemical weapons in Syria by any parties in the conflict”.
[48] Syria invited Åke Sellström and U.N. disarmament chief Angela Kane to visit Damascus for foreign-minister level talks on conducting a probe of the Khan al-Assal attack.
[49] The Russian UN ambassador Vitaly Churkin delivered a report with analysis of the samples taken at the site of the chemical attack, to the UN Secretary General Ban Ki-moon.
[6] The UN mission returned to Syria for five days to conduct fact-finding activities relating to alleged chemical weapons incidents including that in Khan-al-Assal.