A large amount of heroin has been stolen from a shipping container that Will County sheriff's police were using to store evidence, police sources say, potentially dealing a setback to prosecutions, along with the county's efforts to stem surging heroin use. One source said four individually wrapped kilos of heroin, potentially worth $500,000 or more, were stolen from the container, which was left outside a sheriff's substation and secured with a padlock. Other sources could not confirm the amount.