I dunno...I'm not convinced of his (CA"s) involvement. If all three were murdered,
I can't really think of a reason why he would want to kill not only Rachel but two friends/witnesses, also. Unless, Rachel was threatening to 'spill' a family secret or something along those lines?
It's not hard to come up with some reasons suitable for any scenario, but pretty hard with reason that's "good enough"... at least for me.
With one victim, it could theoretically take one hit, one push, one accidental "something" that wasn't meant to be lethal but ended up killing the person. With three there just had to be some sort of conscious decision to go for it, with confidence that double (or triple, if after some sort of escalation or accident one was just injured) murder is better solution than any alterative option.
Going with most popular "TT did it in the jealous rage".
With accident or manslaughter - what was on the table for him if he called cops or drove her to hospital telling straight how it happened and that he's sorry about it?
Any serious sentence? Lost of his inheritance? Lost of the parental rights?
If not any reason for him to expect any of that to happen?
What kind of family or really any mystery could Rachel potentially reveal to pose such a threat to her father that he could possibly figure that he has no other choice than to murder her and two local kids?
Any indicators that Rachel would be willing to expose something that could her struggling family into more trouble? Why would she do that? Why would her father believe that she could do that?
I can't see how any cheating or family secret related secret could pose such a threat to TT or CA that they'd choose triple murder to prevent it from being revealed.
All these stories about CA and TT being sketchy, creepy, sexual offenders and so on... getting away with it all the time - if anything they're painting a picture of inividuals that would be actually LESS likely to go for such extremes (as murder) out of fear of being caught.
Cause it's not what people do, whats happening is that more their despicable actions are going unpunished, less they fear consequences.
It doesn't make any sense for me UNLESS there were other significant factors that we don't know about, that would change this dynamic completely.