Well, here are my 2 cents. They may or may not have value.
If I have my timeline straight Chris was probably around the age of 10 when his parents became Christians. Grace Bible Church's first meeting place that wasn't someone's living room used to be a bar, a bar that was not completely unfamiliar to his parents. I remember RC talking about the irony of 'I used to sit on a bar stool over there, and now I'm behind a pulpit up here' or something to that effect.
There is nothing 'wrong' with going to bars. There is nothing 'wrong' with not being Christian, and neither of these acts are going to turn your son into the kind of person who murders his own family.
But, and this is something that was honestly in my head ~15 years ago, maybe Chris already had his outlook on life set by watching his parents live what was by all accounts a very 'worldly' lifestyle. Maybe he was already destined to be more comfortable living that lifestyle than the strict 'oldest son of a respected preacher' that he was thrown into.
Maybe after living what might have felt like a lie for the last 20+ years he couldn't do that any more. A divorce would embarrass his parents, and probably cost him the $100k/yr job that he was very unlikely to ever replace. And he snapped...
That is the only way I can explain, to myself, the CC I knew having done this.