A year-long military-led investigation has concluded that U.S. taxpayer money has been indirectly funneled to the Taliban under a $2.16 billion transportation contract that the United States has funded in part to promote Afghan businesses.

The unreleased investigation provides seemingly definitive evidence that corruption puts U.S. transportation money into enemy hands, a finding consistent with previous inquiries carried out by Congress, other federal agencies and the military. Yet U.S. and Afghan efforts to address the problem have been slow and ineffective, and all eight of the trucking firms involved in the work remain on U.S. payroll. In March, the Pentagon extended the contract for six months.