On April 19, 1995, a truck bomb exploded just outside of Oklahoma City's Murrah Federal Building, killing 168 people. Within a matter of hours, the FBI launched the largest manhunt in U.S. history, identifying the suspects as Timothy James McVeigh and John Doe No. 2, a stocky twentysomething with a distinctive tattoo on his left arm. Eventually the FBI retracted the elusive mystery man as a bombing suspect altogether, proclaiming that McVeigh...