Six US troops were killed today in a deadly betrayal by an Afghan ally, according to NATO officials. The six were participating in a training exercise with members of the Afghan border police when a border police officer opened fire. The shooter was killed in the subsequent gunfight, but his was still one of the deadliest such sleeper attacks in recent months, the Washington Post reports. A senior police official noted that the shooter had been with the border police for two years. "I think the Taliban has worked on him," he said.