Although all have a corrosive effect on field morale and trust, the April 25 confrontation that killed Britton-Mihalo was cause for particular alarm: For the first time, the killer was a member of Afghanistan’s special forces, handpicked from the ranks of its commandos, who are themselves considered an exclusive fraternity: carefully vetted, highly trained, closely watched…

In outposts like the makeshift base in Kandahar province where Zakirullah and Britton-Mihalo were deployed, the punishingly primitive, close-quarters conditions can foster strong bonds — or allow small irritants to fester.

“They work together, they patrol together, they are together all day of every day,” said Col. Bismullah Waziri, executive officer of the Afghan commando brigade. “We are all aware that there are cultural issues. Sure, they are different from us. And we are different from them.”