He abandoned his intersection, leaving the delivery truck at odds with a stalled motor scooter, and began closing the gap. He was twenty yards from the foot of the bridge, fifty from the rising dispute, when he realized that the man in the center of the bridge was not pointing his hand, but rather a gun. He also saw that one of the men backed to the rail was restraining the other with an arm wrapped around his throat.

Kammerer went for his radio, but the frequency was momentarily blocked by someone’s long-winded traffic narrative. He broke into a run, and shouted, “Police! Arrêtez-vous!”

The three men ignored him.

Kammerer finally heard a break on the frequency, but in the heat of the moment, with his heart thumping in his chest, the proper radio conventions and protocols escaped him—just as his instructor in training had said it would. But he remembered what she’d said next: If you forget the correct way, just screw the procedures and say something.

He did exactly that.

“Pont des Bergues, the footbridge!” Kammerer shouted into his microphone. “Officer needs help! I see a man with a gun, possible hostage situation!”

Thirty yards from the trouble, Kammerer slowed his pace and drew his service weapon. Before he had a chance to shout anything more, things began to happen in what seemed like slow motion. The man holding the hostage, the one clad in some kind of black suit, pushed his captive away and produced what appeared to be a gun of his own. Before he could raise it, the man in the middle of the bridge fired once, and then kept firing, a hail of shots that Kammerer would report as ten, but later be proven by ballistics evidence to be six. The man clad in black rocked once, twice, and then twisted back and flipped over the metal rail, disappearing into the river.

Kammerer pointed his weapon at the shooter, and screamed, “Drop the weapon!” He said it three times in all, once in each of the languages he spoke—French, English, and Swiss-German. One of them, he wasn’t sure which, seemed to work. Or perhaps it had more to do with the volume and situation. Whatever the impulse, the shooter set his weapon on the asphalt, backed away three steps, and very slowly dropped to his stomach and went spread-eagle.

“I’m a policeman!” the man shouted in English.

This Kammerer knew better than to take for granted. He kept his gun trained on the shooter as he closed in, kicked the gun a bit farther away, and cuffed the man, all while keeping an eye on the third man who was standing by the guardrail and looking very relieved. Help soon arrived in the form of three other officers, and things began to organize. Kammerer told the senior man, a captain, what had happened.

“Where is the other?” the captain asked. “The one who was hit?”