“ A human rights network of 60 organizations working along the U.S.-Mexico border released a letter to Congress on Wednesday urging them to investigate “shadow police units” that have helped cover up beatings and killings by Border Patrol agents for more than three decades. The shadow units, identified in the letter as “Border Patrol Critical Incident Teams,” are said to possibly be “the largest and longest standing shadow police unit that is operating today in the federal government.” “