In addition to the confession video there are several documentaries about him,mostly made by Canadian TV.If there's anything like a "Jekyll & Hyde" in real life I believe he is one.You listen and watch Ted Bundy and you quickly realize that he's utterly amoral..completely devoid of conscience.IMO that's not the case with Williams.He's clearly capable of savagery but also seems to be capable of genuine decency.
Of course I could be wrong about the decency.
I would guess that you are probably right. Which may be why that confession was so unnerving to watch as it unfolded.