Okay, so the way the story is being told is that Derek wanted to see his little brother, TJ. According to one of Chessie's sisters (FWIW), TJ was released from jail earlier on the same day that Derek turned himself in.
The same sister has recently commented that her now deceased husband was the last person to see Brittney, FWIW. Sorry I can't link, but it is a FB comment of hers on a public page, FWIW.
Derek was in jail when Brittney disappeared, but I think it is a reasonable assumption that he knows quite a bit about many of Brittney's past activities. It's also very possible that he knows quite a bit about his funny uncles and some of their proclivities and activities.
If he goes the route of sharing information with BCSO, it could help the investigation of the sexual abuse as well as Brittney's disappearance.
My opinion is that he is at a crossroads. He can honor the victims by giving up some truths or honor the [alleged at this point] perps by keeping the silence.
MOO.