I am now leaning towards the possibility that there was no extra bag of clothing. It appears now we are being led to believe the clothing in the bag was what Sierra was wearing.
So we now may have a perp who harmed her and took the clothes to a shed on Laguna.
The problem I have is why. Where are her shoes, socks, jacket, etc? There was a T-shirt, pants and underwear in the bag. If she walked out of the house that morning, she would have had on shoes and outerwear also.
Since the clothes were folded neatly and placed in the bag, it almost appears as if the perp was leaving a gift for the family and this was as close to the home he was willing to go.
This makes sense to me. Re: her shoes. With all this talk of searching the percolation ponds, I have to ask: Wouldn't waterlogged shoes help her sink? I know that boots would.