THE THREATS AND vandalism pale, however, before the April 19, 1995, bombing of the Alfred P. Murrah Federal Building in Oklahoma City. The blast killed 169 people, including 19 children in the day-care center on the building's second floor. More than 600 people were injured. It was the worst terrorist attack in U.S. history.

Because of the way the bombing was accomplished—using a truck filled with explosives—investigators first suspected Arab terrorists, since this method is a signature of some Middle East terrorist groups. The public, too, was quick to jump to the same conclusions, and for a short time, there was a flurry of hate directed at Arab Americans on the streets and on the airwaves.

What kind of American"

Within hours of the blast, however, federal investigators found what one expert called "an indelible trail of evidence" leading to...