Abdel Hameed Alyousef, 29, holds his twin babies who were killed during a suspected chemical weapons attack, in Khan Sheikhoun in the northern province of Idlib, Syria, April 4, 2017. Legal and moral taboos were shattered with the use of chemical weapons during Syria's civil war. Hundreds were killed in poison gas attacks widely blamed on President Bashar Assad’s forces under the protection of his chief ally, Russian leader Vladimir Putin. Several years later, concerns are growing that such weapons could be used in Ukraine. (Alaa Alyousef via AP, File)
