The many images from Syria of dead children and despairing civilians have left the world all but numb to the horrors of the country’s more than six years of civil war. But a chemical attack on Tuesday demands attention as much for the heart-wrenching pictures and videos of the victims as for the need to determine who was behind it and hold them accountable. A war crime has been committed, one so cruel that to do nothing, as has happened too many times during the conflict, is to give tacit approval for even greater levels of barbarity. An investigation will be necessary to find out who was behind the attack in Idlib province, held by rebels fighting to overthrow Syrian President Bashar al-Assad’s government. At least 80 people were killed, many of them children, and hundreds injured by what is thought to have been a nerve gas, possibly sarin. Humanitarian workers and the rebels blame Syria’s air force for dropping the chemical, but the claim has been denied by Assad’s government. Russia, Syria’s ally, said the gas resulted from a bomb falling on a rebel arsenal of chemical weapons. ‘I couldn’t save anyone. They’re all dead now’: Syria gas massacre claimed 22 members of one family Chemical weapons have been regularly turned to during the conflict, despite their use being banned under international law. Assad agreed to destroy stockpiles in 2013 under threat of attack from the United States after up to 1,300 people died in a sarin gas strike in the Damascus district of Ghouta. He has denied using such weapons, although the difficulty of producing them makes accusations that they are solely being deployed by rebels hard to believe. A United Nations Security Council report last year determined Assad’s regime was carrying out chlorine attacks on civilians, but a resolution among members for sanctions was vetoed by Russia and China. The US, despite threats of action, has done little, although President Donald Trump, in condemning the latest attack, hinted at a shift. The failure of the Security Council to act collectively requires a government to step forward and take the lead. The world cannot stand by and do nothing. Allowing impunity would have further catastrophic consequences for Syrians and innocent people caught up in combat zones elsewhere.