One thing I've noticed in cases like these, is that the killer has come up with a "perfect plan", which they believe no one will ever be able to figure out and prove anything, and will let them carry on their life as they'd prefer to live it. IMO they only commit the murder because they have convinced themselves they'll get away with it.
That's in contast to many other murders that are committed in haste, or under intense emotions, that police can much more easily solve.
I really wonder if there was a moment, and when it was, that CW thought to himself: gee, these oil tanks would be a perfect place to hide a body.
And how much does having that 'perfect plan': whether it's staging an accident and letting yout child die in a hot car (Ross Cooper), getting your best friend to stage a break-in that results in your wife's death (Mark Sievers), hiding your wife's body in your home's secret septic tank, 'the perfect place to hide a body, the previous owner said' (Ian Stewart), how much does having the possibility of that plan in mind, encourage the killer to go ahead and do it?
Are these people, in part, strongly attracted to the idea of carrying out this secret plan and getting away with it? Is that part of the motivation: "I could do this: wouldn't I be the clever one, then. I could fool them all." A kind of power trip.
