The linking of his DNA under KV's fingernails while KV fought for her life (he's skinny, not well built so she could at least fight back) AND his being taken to the ER the following day for treatment of scratches and poss a hand injury is deadly for him.
Also, he put himself right in the area of the park where the "puddle" is (he wouldn't know about that being there all year-round unless he was in that spot in the weeds) with her.
I saw a video (sorry no link handy) where the father was asked again about the hospital visit and his scratches. This time he skirted the question. Son may have given different explanations to others as the explanation of his scratches & injuries, too and I'm sure Legal Aid Team has spoken to them about this.