I'm not convinced JC gets a pass just yet, despite turning KY in. JC was there when KY burned the vehicle, drove him down to Edwards. But let's not forget the police stop. There were guns in the vehicle as JC was trying to avoid getting stopped by the police while speeding and swerving all over the road. I'm thinking JC may have thrown KY under the bus to cover his own butt, maybe in order for a lesser charge on another case or possibly he was originally going to help KY out, but once he found out that law enforcement was on it, he didn't want to get pinned with the crime, so he may have ratted him out. To me, it doesn't seem like the normal set of circumstances for turning someone in.
You may be right. I think he likely gave it some good thought on his way out of Edwards after dropping KY off at his residence there. I'm sure the thought crossed his mind that if they had been stopped only a few hours later, when reports of Jessica missing really started to spread out, he could have been picked up for aiding and abetting a murderer. If he hadn't called, and police found out he was an accomplice, he could be charged and serve life in prison. But, he did also call the police on the 10th, and seems to have cued them into where KY was staying. It may not matter to police that he did some shady things along the way. It may just matter to them that they've finally got KY right where they want him.
We also have to consider that he may not have been in the most rational of mindsets. His brother had just called him and told him that he committed a murder and put a body in the woods and needed helping disposing of evidence. If JC didn't know the truth about Kara and was just giving KY the benefit of doubt for the last ten years, that phone call cemented everything that everyone has been saying about his brother all along. It had to be shocking to go to him and see his scratched face, witness him burning himself, and then having to contend with the idea that if he stepped out of line or went against his brother, he could be the next victim.
He seems to have done what he had to do at the time. Once he got KY where he needed to be, he likely considered the consequences of being involved in such a coverup, what it would mean for his family, and the potential of what his brother might be - a serial killer with a temper a mile long and nothing to lose. This is all JMO, of course, and only based on what I've read in the court docs and concluded based on that. Not saying that JC is a saint or anything - he's clearly proved otherwise. Only he knows what really happened between him and his brother that night.
Per case.net, JC appears to still be going through the system regarding that stop for reckless driving, resisting police stop, etc. last year. So he's definitely not out of the woods. But LE does need his witness testimony to cement their case. I would guess they've offered him some sort of immunity or at least a lesser sentence for him to give up information. Again, all JMO.