The Chatham County District Attorney's Office is making changes to how it prosecutes marijuana cases.On Wednesday, Chatham County DA Shalena Cook Jones announced, effective immediately, her office will not prosecute cases involving possession of less than an ounce of marijuana.TRENDING STORIESTexas school shooter purchased AR-15 made by Coastal Georgia gun manufacturer: ReportWhite House names Savannah Police Chief Roy Minter finalist for U.S. Marshal jobTwo monkeys and a massive snake on the loose in Effingham CountyThe decision comes after the Georgia Bureau of Investigation said it would no longer test any green leafy substance weighing less than an ounce, unless felony charges are involved. Without a verified test, it's difficult to determine whether the substance is illegal marijuana or legal hemp.The DA's office says, without the ability to test the substance, it would be impossible to prove its unlawfulness at trial. There are exceptions to the rule and the DA's office says it will continue to examine each matter on a case-by-case basis.