It could've been ISIS, as the leaders went there to hide while DJT/Putin took them out in the Middle East.
However, we know that ISIS qas creatwd by, and controlled by, Bummer. So by extension, the USA is responsible.
https://www.independent.co.uk/news/world/europe/isis-leaders-ukraine-tukey-syria-caliphate-al-bara-shishani-a9211676.html