A trainee in the Afghan border police turned his weapon on his NATO trainers Monday, killing six. The attack, which occurred near the Tora Bora Mountains on the Pakistani border, is the fifth such incident in 13 months. The Taliban has claimed responsibility for the attack, claiming that the shooter joined the Afghan police force for this purpose. All six victims were American. The incident highlights the difficulties in NATO's plan to train Afghans to run their own security forces over the next few years.