Put his ass up against a wall and get five really poor shooters, on full auto, and let them fire away. The poor quality of their marksmanship will cause many bad wounds and much suffering. Then send up someone with a pistol and start on his elbows, shoulders, knees, feet and finally between his ears. No trial needed.
He could stop it if he dimes out every member of his rotten organization. They might just stop doing this to him. (five hours of sincere confession later). We said ‘might’.