Jer 17:9 The heart is deceitful above all things, and desperately sick; who can understand it?
I'm not saying murders like you mentioned above are not demonization...what I'm saying is despite the removal of Satan as per Rev 20...
1Then I saw an angel coming down from heaven with the key to the Abyss, holding in his hand a great chain. 2He seized the dragon, that ancient serpent who is the devil and Satan, and bound him for a thousand years. 3And he threw him into the Abyss, shut it, and sealed it over him, so that he could not deceive the nations until the thousand years were complete. After that, he must be released for a brief period of time......men will still have an evil heart. Perhaps tempered a bit without Satans influence but still capable of evil.