To be honest, I don't think BK gets any pleasure from the families' anguish.
I think the pleasure he gets from the trial is getting to watch the whole criminal justice practice from the inside. To see how the investigation and trial unfold and compare them to ones he studied in his coursework. To take pride in parts of it that he feels he got away with (like things the prosecution doesn't bring up or specifically says they don't know....or perhaps even small things they get wrong).
He's disconnected from seeing other people as actual people with very real feelings. The girl or girls he targeted weren't "people"....they were symbols, IMHO. I don't feel he attacked, say, MM, because he felt like she ignored him when he tried to chat her up in the grocery store. It wasn't about who she was, it was about what she was.
And when you see other people as a mean to an end, a way to work out your issues, then they become isolated in your mind---you don't see them as a daughter, friend, relative to other people.
His taptalk posts referred to beginning to see other people as sacks of meat with no self worth, like he viewed himself. He talks about his parents' worry, anger, and upset not even registering with him.