Your theory certainly ticks a lot of boxes, IMO !! I get impression that the murders happened at that house, also.
The only thing I might query is to how TT would have known Rachel was shopping with California Jacket guy that day, in the pre cell phone era. Maybe he had his suspicions about by him by then, anyway, and just put ' two and two' together.
With the method of disposal that you have suggested it would mean that when he was interviewed by police he had nothing fear as sadly the bodies were already gone.