Maybe CA was always covering, and GA had enough (which implies GA was very in tune with how out of line KC had gotten)-he should have known immediately that KC took the gas, but he also knew CA would cover for her and GA was tired of the stress of the constant disagreement with how to handle KC. Remember he said he followed up on the Sports Authority job, maybe he wanted to use that knowledge to assert himself with KC-but he either kept it to himself, or CA shelved it.
So he "innocently" called police, something he could easily explain to CA later as if he didn't mean to get KC involved, yet at the same time KC could get busted by LE with whom CA could not negotiate. Had he called police about the credit cards before this time, CA would have been very unhappy.
GA may have loved his daughter, but I do not think he liked KC at all, he says a few times in interviews that KC was the cause of the problems in his marriage.
I know in my own household, often mom was the empathy and dad was the reality-but when they disciplined, they were always united. Thank God for dad, his expectations helped me be a responsible adult, and I sure needed mom during my pitfalls. In the A household, this system was very out-of-whack, GA maybe wanted to act like a dad, be the king of his castle, but CA was determined to cut him out of that. Why? Had GA ever overreacted/gotten physical or verbally abusive with the kids, and CA did not trust his parenting/overprotected her kids? Or is CA just that controlling? Okay, yes I know that CA is that controlling......
None of the above prevents GA from involvement after-the-fact-I think he wanted KC to be held responsible for theft and utter disregard for others, but not for murder.
ETA: I know the above reads like CA overpowered everything, but don't get me wrong....GA should have manned-up and BEEN a dad. He would have been doing the right thing to ignore CA sometimes and follow-through with KC, and CA would have appreciated it later.