Yeah, on the surface he was a corrupt rapist and was enslaved by the demons this whole time, but what do we know about him pre-enslavement? Maybe before the demons appeared he was actually a noble leader and loved by many, but had hidden desires he kept locked away for the good of those around him and the demons just brought those desires to the surface. You see how he acted at the end? Point is, if he was murdered like that, we'd never know the truth, which could be a key point in tracking and taking down the demons.