As soon as I read that it seemed quite alarming.
One thing I can't get past is the fact that WM had his pool filled in not long after Cindy's disappearance.
I don't know whether Cindy made it to her estranged husband's house and was killed there (in which case the car must have been staged) or a hand off of Nicholas did occur in the Abbey parking lot and domestic violence ensued. (Perhaps WM was angry about having to deliver Nicholas instead of having him picked up.)
Either way, if you have an in-ground pool in your yard, then you already have a hole that's eight feet deep. It would be difficult to dig a sixteen foot hole, but if you take a sledgehammer and break a hole in the bottom of your pool, then it might not be that hard to dig down another eight feet. Then you end up with a hole that's sixteen feet below ground level.
Even though LE dug up WM's backyard several times, I'll bet that they didn't think to look underneath the pool.
This is just a guess, but if someone held my feet to an open fire and forced me take a guess as to where Cindy is, I would say that she's buried in WM's backyard, about 16 feet deep, below the bottom of the old swimming pool.
It's possible that WM wasn't involved, and it's possible that he paid one of the ex-cons at Sterling Axle to get rid of Cindy for him—there were plenty of guys there who would have done it for a hundred bucks—but domestic violence (pre-planned or otherwise) seems like the most likely explanation for Cindy's disappearance.
I hope I live to see the case solved and to see Cindy's remains recovered.