“At its best, accountability completes mercy in generating justice. It does so by meeting a humane restraint of power (on the part of those in the position to punish) with a humane exercise of power in return (on the part of the person who caused harm). Justice, then, exists when all parties exercise their power in a way that is consistent with the humanity of everyone involved and in the interest of the greater good. In the aftermath of violence, mercy plus accountability equals justice.”