Of all of those charged, DK was the most likely to confess, so now that he has done so, I fully expect him to come clean about the involvement of the others as far as the sex crimes go, but I'm not too sure about him having any knowledge of what happened to Britney.
I've always held the opinion that he is somewhat simple minded, and as such, they wouldn't trust him with any real knowledge. I do hope, however, that he heard some talk and speculation that Britney was becoming a problem (concern that she may tell LE about the sex crimes) and he has told authorities what he heard. He would have known for example, if there was genuine concern with her disappearance, or if they were mostly relieved. Did all the (Wood) family members plan to do whatever they could to find her, or was there a general acceptance that it was sad, but futile to search for her?