British prosecutors declined to bring charges against the officers involved in the killing, a decision that provoked outrage among human rights activists and civil libertarians around the world. Gabriel knew that, under similar circumstances, he could expect no such leniency. It meant he would have to be certain before acting. He was confident of one thing. He believed the bomber, like a painter, would sign his name before pressing his detonator switch. He would want his victims to know that their imminent deaths were not without purpose, that they were being sacrificed in the name of the sacred jihad and in the name of Allah.

For the moment, though, Gabriel had no choice but to follow the man and wait. Slowly, carefully, he closed the gap, making small adjustments in his own course to maintain an unobstructed firing lane. His eyes were focused on the lower portion of the man’s skull. A few centimeters beneath it was the brain stem, essential for controlling the motor and sensory systems of the rest of the body. Destroy the brain stem with several rounds of ammunition, and the bomber would lack the means to press his detonator button. Miss the brain stem, and it was possible the martyr could carry out his mission with a dying twitch. Gabriel was one of the few men in the world who had actually killed a terrorist before he could carry out his attack. He knew the difference between success and failure would come down to a fraction of a second. Success meant only one would die. Failure would result in the deaths of scores of innocent people, perhaps even Gabriel himself.

The dead man passed through the doorway leading to the piazza. It was far more crowded now. A cellist was playing a suite by Bach. A Jimi Hendrix impersonator was grappling with an amplified electric guitar. A well-dressed man standing atop a wooden crate was shouting something about God and the Iraq War.