Perhaps, if we're subscribing to the theory someone has had a hand in disposing after the fact. It's probably highly likely he's just dumped her stuff under his bed and his family members have raised his bedroom to the ground before police were able to get access.I now really don’t think he disposed of some of the items, I think others did a far better job than he cared to do, and I don’t believe they knew until after her body was found, otherwise I don’t think she wouldn’t have been found either. IMO obviously.
I don't know why I think it, I just get the impression he didn't intend to kill her, and when he has he's probably tried various ways to get rid of her and hide the evidence, hence the attempt at dismemberment. Perhaps even researching what to do. After realising that isn't happening he's just lost interest.
I still believe her clothes would have been a significant discovery. Could it really be the element of luck has potentially kept him out of prison? Because that sure is some feat for a kid.