The man who murdered President Hamid Karzai's half brother, one of the most powerful people in Afghanistan, was a U.S. ally. Sardar Mohammad commanded several hundred police officers, and he helped arrest scores of Taliban fighters. He also shared intelligence with Americans. It's not known what prompted Mohammad to kill Karzai, with whom he was close. The Karzai family says Mohammad traveled to Quetta recently to meet with Taliban insurgents, and Mohammad's officers report that he was acting strangely over the last several weeks.