Interesting redbundy, the reason you think TH does not fit, is one of the reasons why TH fits best IMO.
Was the place where the bodies were found ?
A). The scene of the crime.
B). The disposal site.
C). A staged crime scene.
If it was the scene of the crime, where were the bikes at the time of the crime.
1). In the direct vicinity , hence the boys took the bikes into the woods via the service road or Blue Beacon truck wash, or from the Devils-den area, or over the pipe bridge (highly unlikely IMO). There were bike tracks in the woods, but I did not see any evidence that the bike tracks were directly linked to the boys bikes.
2). The bikes were hidden in the vicinity of the pipe bridge before the boys crossed the pipe bridge. Stevens bike was brand new, he kept it in the spare bedroom. Would he have left it unattended ? I don't think so. Christopher was even frightened to cross the pipe bridge as told by his stepbrother Ryan.
3). The bikes were at a totally different location as the boys were in the woods.
If the bikes were in the direct vicinity during the crime, I don't see a single reason to dispose the bikes at a different location. A stranger would not have anything else on his mind other than to get out of the place as quickly as possible. They would throw the bikes into the ditch with the bodies & clothes or just leave them where they are. Furthermore, a stranger coming in from the truck wash or truck stop would not even see the bikes if they were hidden over the other side of the pipe bridge.
If the bikes were hidden in the area of the pipe bridge then only someone who could associate the bikes with the boys would have a reason to throw them into the Bayou. There is also the possibility that some sort of prankster who had nothing to do with the crime just lobbed them in.
If the bikes were in a totally different location, only some one who could be linked to this location (and thus to the boys) would have a reason to move the bikes.
As far as the bikes go, I see some things that are quite unusual as far as Hobbs is concerned. A short time before the boys were murdered, Stevens bike was stolen from the Hobbs home. TH did not want to buy him a new bike, so his grandfather bought him a new one. In his police interview and on other occasions Hobbs was constantly referring to Stevens "new bike" in situations where it felt out of place. Hobbs had not seen the boys all day. The bikes were where the boys were, if he had not seen the boys then he had not seen the bikes.
My speculation: The bodies were placed in the ditch via the service road (eastern side of the ditch) and the bikes were later (or earlier) transported on a separate journey. The ditch scene was staged to make it look like someone from the truck wash/stop had killed the boys. It was too dangerous to access the ditch a second time so the bikes were thrown into the Bayou. If anyone had seen TH with the bikes he could have told the police he had just found them, after all one of the bikes was his stepsons. The ditch could be accessed directly with a truck, where as the pipe bridge had to be accessed via a short footpath from either side.
As far as staging things go, I've seen some find examples of this from Hobbs.
On the contrary to what some other posters are saying, TH was not investigated, and the Hobbs home was not searched. Only at a later stage were the Byer's or the Moore's home searched.
I don't deal in absolutes, these are just my thoughts.