Why does Darin defend Darlie?

Hi all,

I'm sure this has been addressed else where but I couldn't find it. So obviously my question is why would Darin defend Darlie? I understand that it could be 1. Because he believes she is innocent, or 2. He in some way was involved in the murders. However, if he were involved in murdering the boys, why wouldn't Darlie rat him out?

Thanks for your input.