The vignette was charged with drama. A government informant had wheedled his way into radical Islam’s inner sanctum: the Jersey City apartment that served as home and haven for “the emir of jihad,” the honorific by which Omar Abdel Rahman, the infamous “Blind Sheikh,” was known to his worldwide following. Here, he conducted meetings, issued directives for his Egyptian terrorist organization, and was briefed by the jihadist cell he had established in the United States, the operatives of which required his edict—or fatwa—before they could execute attacks.

The informant was there to outline a plot then underway: simultaneous strikes against the United Nations complex, the FBI’s lower Manhattan headquarters, and the Lincoln and Holland Tunnels. It was May 1993, and New York City was already reeling from the same terror cell’s bombing of the World Trade ...