Investigation into the use of Chemical weapons’ by Islamic State in Iraq

Islamic State fighters seized Iraqi cities and declared a self-styled caliphate in a large swath of territory in Syria and Iraq in 2014. The group was formally declared defeated in Iraq in 2017 following a three-year bloody battle that left tens of thousands dead and cities in ruins. However, its sleeper cells continue to stage attacks in different parts of Iraq. U.N. investigators are compiling evidence on the development and use of chemical weapons by Islamic State extremists in Iraq after they seized about a third of the country in 2014, and are advancing work on the militant group’s gender-based violence and crimes against children, Sunni and Shiite Muslims, Christians and Yazidis, the head of the investigative team. What should be the punishment for countries which uses chemical weapons against civilians ?