Your suggestion of an indictment against Saddam is good. But the US will not seek such an indictment because of their complicity in the war crimes of the Iran/Iraq war.
Iraq started a war it couldn't finish due to Iranian human wave attacks. US wanted Iraq to win and supplied satellite intelligence as to where the human waves were amassing, knowing full well that Saddam would use chemical weapons.
Anyway, what is this obsession with chemical weapons? How is it any worse than to die or be maimed from the burning shrapnel of carpet bombing?
US opposes chemical weapons because it reduces the technological advantage the US possesses when using conventional weapons. Nothing to do with humanitarian reasons.