Conyers Police arrested Tasmiyah and Jasmiyah Whitehead Friday. It followed a four-month investigation. The two are charged as adults with the murder of Jarmecca Whitehead.
She was found stabbed to death in January.
Conyers police chief Gene Wilson says authorities suspected the pair early on. He said the two had told authoriites they found their mother dead and ran for help.
He says authorities have no motive.
Wilson did not immediately return a phone call.