A Time to Kill, a Time to Die — Charles Ray

Henry Waylon spent ten years on death row, before finally being executed. A day after his death by lethal injection, DNA evidence shows that he was innocent of the crime for which he'd been convicted. The judge who sentenced him to die receives a threatening note, and hires Al Pennyback to find out who is threatening him. As Al digs into the background of the crime, he finds that there's more to the case than meets the eye, and, when people associated with it start to die, he finds himself in a race against time to catch a ruthless killer.