Human Rights Watch says the Syrian government repeatedly and systematically deployed the chemical weapon chlorine gas against residents in Aleppo during the final weeks of a siege and battle to retake the city from anti-government rebels late last year. The report, released Monday, accuses Syrian military helicopters of dropping chlorine gas canisters on residential neighborhoods at least eight times. Last week, Amnesty International published a shocking report accusing the Assad government of engaging in a “deliberate policy of extermination” by hanging thousands of civilians at the Saydnaya prison near Damascus.