While murder is the worst of all crimes and should bring great sadness, what you say about the perp, unfortunately, simply provides fuel for more murder.  Your ability to dehumanize another is exactly how killers legitimize their actions.  If we tolerate dehumanization for any reason, we teach others to do the same to us.  While the perp must receive punishment, the failure of the perp should bring sadness.  Two lives were lost in the murder.  Murder must be prevented, but by relishing the perp's suffering, you teach and legitimize the process for all (IMHO).