One Shot

A lone gunman hides in a parking garage and shoots into a crowd. Five random people die in a senseless massacre. The shooter leaves a perfect trail behind him and the police quickly track him down - it's a watertight case. But after his arrest, the gunman refuses to talk. Then, to his lawyer, he utters a single phrase: "Get Jack Reacher for me." But Reacher is working on his tan with a Norwegian blonde on the beach in Miami. He was in the machine his whole life. Then the machine spat him out. Now he dozes on buses, watching the passing scene, observing the chaos of America. What past event connects this wandering ex-army cop with an obvious psychopath?