A group of human rights organizations have submitted a criminal complaint in Germany on behalf of chemical attack victims in Syria, asking federal prosecutors to investigate and eventually arrest those responsible for some of the deadliest gas attacks in the country’s civil war.

On Monday, the Syrian Archive, the Open Society Justice Initiative, and the Syrian Center for Media and Freedom of Expression submitted to the German federal public prosecutor a dossier of evidence they say confirms the Syrian government’s use of the deadly nerve agent sarin on its own people.

The filing asks Germany to investigate an attack in the Damascus suburb of Eastern Ghouta in 2013 and another in the northwestern town of Khan Sheikhoun in 2017. The nongovernmental organizations say the body of evidence they have compiled contains new information about the attacks, which together killed some 1,500 people, many of them children.

Syrian President Bashar al-Assad denies using chemical weapons during the country’s long-running war despite a body of evidence from rights organizations, journalists and medics documenting otherwise.