JOHANNESBURG, SOUTH AFRICA – They were given marijuana to dull their senses and alcohol to increase their rage. But after months of carrying out a campaign of terror against government-opposition supporters, even the haze of intoxication was not enough to hide the horror of their actions. "First they gave us dagga [marijuana]. We smoked dagga and smoked dagga and then we got drunk. Then we burned the houses, took the cattle, and beat people," says Henry, a teenager and former member of Zimbabwe's feared National Youth Service. Henry fled to South Africa and is now living on the streets of...