I'm very much on the fence on whether she was there on the 7th. These are experienced investigators, cadaver dogs, and many citizens, who helped search for this child, and have stated that they did look inside the culvert. It would only be natural that they would being it was so near the home.
They didn't see her on Day 2 of the search, one LEO confirmed, and he'd personally looked in that culvert. A private citizen, came forward to the site, to tell LE that they looked, what dates, and that they saw nothing in the culvert. No one who has been searching, and looked in the culvert, saw anything in there, not even trash. Then, there was an odd incident, behind the homes, near the culvert, the night before they found the body.
As far as odor, and decomp, we do not know if only the body was found in the culvert, or if the body was placed in a bag of some type, to keep the odor from attracting attention. If so, it could be easily moved.
In the statement that LE has released, nowhere does it say, where WM took SM, only that he admitted to removing her body from the home. (OT, but one thing that has bothered me, a lot, about his second statement to LE, is that it says he "believed" her to be deceased. He's not in the medical field, she may have had only a very faint pulse, and he just couldn't feel it. He wasn't going to call the dr. anyway, but thinking she may have been left out there, even for just awhile, well, really bothers me. I wish there were some way to know for sure. )
Apparently cadaver dogs did not hit on anything prior, yet, a private citizen's dog alerted on 10/22, as did a LE cadaver dog. I
have to wonder, especially after they had searched the field at the college, on 10/07, where officers found "items of interest" there that day, if they got close, and he got worried, and somehow had the body moved. He'd likely think that they'd not go back over that area as it had been so thoroughly checked before.
I've attached a pic of the culvert, and a link to a Five Fast Facts article from Heavy. Fact #2 has photos and video of LE retrieving the body, and statements made by people who came forward to tell LE that they'd searched the area, and that culvert, and nothing was there prior to the 22nd.
Culvert is straight through and 100' in length
w/o any debris, other than a rock. The child's body was discernible that day, from a rock. If she was moved, then he'd have to have had help as he's on an ankle monitor.
See Fact #2
https://heavy.com/news/2017/10/sherin-mathews-body-father-arrested-texas/