Jack Reacher one shot

Six shots. Five dead. A heartland city thrown into terror. But within hours the cops have it solved. A slam-dunk case. Apart from one thing. The accused gunman refuses to talk except for a single phrase: Get Jack Reacher for me. Reacher lives off the grid. He's not looking for trouble. But sometimes trouble looks for him. What could connect the ex-military cop to this psychopathic killer?