I honestly think that either he did it, or knows who did.
One thing we can all agree on is that he wants to be the one who murdered JBR.
He may not actually know the person. (I don't really know you all) but he has had some contact with them. It would be impossible for me to find out who you were, but he would know that the authorities could/would do just that.
IOW he may be the key to solving the problem and that's why the DA is bringing him in, to help them unlock the door.
BTW I think the Ramsey's left their door unlocked or someone put a piece of tape on in to keep it from locking when they left. The perp came in the front door. JMO