On Aug. 17, 1988, the Pakistani presidential aircraft, codenamed PAK-1, plummeted out of the sky into a dusty field outside Bahawalpur in southeastern Pakistan. Within a matter of hours, I found myself overlooking the still-smoking crater that the C-130 Hercules aircraft had dug into the earth in a region near the Pakistani border with India. The investigation that followed, long before the days of instant internet and cellphone communications, may have been the most complex I'd ever worked in my career as special agent for the U.S. State Department....