And for MS the pleasure would be enhanced by the fact that TS would have no idea what he was planning. Every argument, disagreement, rebuff, putdown, etc., added to that pleasure. My sense thus far is that for CWW this was more of a straight-ahead business proposition, combined with a favour to his BFAM.
Interesting that "the reason" in these cases ostensibly involves the kids. Dan Markel, Kelsey Berreth, the Watts family, TS -- for the sake of form it has to be a child's life in peril, and not the selfish desires and interests of the murderer(s). Because then it's for the greater good, moral qualms (if any) can be abated. Not murder, after all, but a form of self-defence.