A military investigation has found that the U.S. is in part responsible for killing 24 Pakistani soldiers in an errant airstrike along the Afghanistan border on November 26. The report also blames Pakistan for firing on U.S. and Afghan troops, saying the joint team returned fire in self-defense. The findings come at a time of deep mistrust between the two strategic allies. Adam Entous, national security correspondent for The Wall Street Journal, reports on the latest developments.