SUVs and sedans in question land in sealed containers headed for Afghanistan under the Afghan Transit Trade Agreement (ATTA), which are not subject to scrutiny under international law. How they cross the international border in sealed containers and then land at the various yards mentioned afore is a complex question involving geo-political realities, socio-economic difficulties along with a host of other myriad factors. This will remain a million dollar question, unless factors mentioned above do not undergo structural changes. More simply put, if you provide people involved in this trade with better alternatives, they will let go of this trade altogether.
