A/HRC/36/55 Furthermore, the OPCW FFM was able to confirm by comparative DNA analysis that two individuals who had been the source of blood samples taken in Syria without the OPCW FFM team present were identical to two patients who had given blood samples in the neighbouring country in the presence of the OPCW FFM team. The Designated Laboratory results of the biomedical samples taken from these two patients on both occasions were consistent, and showed exposure to sarin or a sarin-like nerve agent. This DNA test together with the laboratory findings confirms that there was a link between the individuals from whom biomedical samples were taken in the neighbouring country in the presence of the OPCW FFM, the site of the alleged attack, and the witness testimony. 23. Taken together, the epidemiological data available, the clinical symptomatology reported, the laboratory results of autopsy and biomedical samples taken from alleged victims, and the identity confirmation of two individuals samples of whom had been collected in the presence of the OPCW FFM subject to full chain of custody procedures as well as in biomedical samples collected at medical facilities in Khan Shaykhun 19 leave no doubt that sarin or a sarin-like agent had been released in Khan Shaykhun on 4 April, and that it killed or injured these victims. 24. The OPCW FFM could not independently verify the provenance of the additional samples it received from third parties. It attempted to corroborate the information about the collection of these samples by testimony and by verifying accompanying documents including photographs and videos taken at sample collection. The OPCW FFM reported that, although it was not in a position to categorically verify the entire chain of custody of these samples, the testimony and documentation submitted alongside the samples provided a good degree of confidence. 25. The analysis of biomedical specimen received from the Khan Shaykhun Medical Centre (blood, liver tissue, lung tissue, and hair samples taken at autopsies from three fatalities) undertaken by two OPCW Designated Laboratories confirmed exposure to sarin or a sarin-like substance. 26. The results of the analyses of the additional environmental samples (animal parts, vegetation, and soil from the impact area) showed chemical signatures consistent with a release of sarin or a sarin-like nerve agent: the presence of primary and secondary degradation products of sarin in environmental samples; fluoride regeneration of sarin and the detection of a tyrosine adduct in biological samples confirming the exposure of the dead animals to sarin or a sarin-like agent; and the detection of by-products of sarin synthesis and certain other characteristic impurities in the environmental samples. 20 27. The OPCW FFM also received environmental samples (soil, metal fragments, bone, vegetation, and extracts) from the Syrian government, together with a video recording of the sample collection. An unnamed volunteer from Khan Shaykhun had reportedly provided these samples to the Syrian authorities, and the samples had been analysed by the SSRC Barza. The OPCW analysed these samples at its central laboratory in Rijswijk, the Netherlands. Results of the analyses by the two laboratories (OPCW and SSRC) were broadly consistent, showing the presence of sarin and impurities related to sarin synthesis and characteristic degradation products. Both laboratories also found hexamine in some of the samples.21 The presence of hexamine was not further explained by the OPCW FFM, but the chemical had also been found in environmental samples collected 2013 after the Ghouta incident. Two competing explanations have been offered in the past to explain the presence of hexamine — either the chemical might indicate the use of an artisanal explosive (RDX) for agent dispersion, or it had been used in the sarin synthesis as an acid scavenger. While the former explanation cannot be ruled out, the latter would be consistent with the chemicals declared by Syria in 2013 to the OPCW as part of their chemical weapons stockpile,22 as well as with the process used in the past by the Syrian army for employing 19 20 21 22 OPCW FFM report, paras. 5.90-5.95. OPCW FFM report, paras. 5.99-5.102. OPCW FFM report, paras. 5.103-5.106. OPCW request for expression of interest (EOI), initially posted on the OPCW website on 20 November 2013, EOI reference OPCW/CDB/EOI/01/20913, OPCW document S/1142/2013 of 22 27