«The Kill Clause» by Gregg Hurwitz

Tim Rackley, a deputy U.S. marshal, watches helplessly as his daughter's killer walks free on a legal technicality. He is suddenly forced to explore his own deadly options – a quest that leads him into the welcoming fold of "the Commission."

A vigilante group made up of people like himself – relentless streetwise operators who have each lost a loved one to violent crime – the Commission confronts the failings of a system that sets predators loose to hunt again, cleaning up society's "mistakes" covertly, efficiently, and permanently. But Rackley soon discovers that playing God is a fearsome task. When his new secret life starts coming unwound at an alarming speed, he is suddenly caught in the most terrifying struggle he has ever faced – a desperate battle to save everything left that's worth fighting for.