Tracking the illicit traffic in weapons

An assault rifle is shipped to a foreign government in the mid-1970s. Forty years later, with the original records of its sale long since disposed of or lost, it is stolen from a poorly guarded stockpile, and driven in the back of a truck across a thousand-mile-long border. It is passed on to a foreign insurgent group, discovered at a Customs post while being smuggled across another border, and is finally seized and placed in a Customs storeroom for investigation or disposal.