In terms of cordoning off the area, phorensic examination of the bench was done on the first day. If nothing was found from that, and nothing was found from the search of the area, including by the dogs, it cannot be treated as a crime scene as there is no evidence a crime has been committed there.
That doesn’t mean that it can’t be thought that there might have been a crime, just that they can’t declare it a crime scene.
If the police had said “sorry, we have absolutely no idea what happened here,” they would be criticised for that as well. The river is by far the most likely possibility, not only because there was a river, but because of the tiny window of opportunity, in an area which was well known to be well frequented by dog walkers.
But a body could take weeks or even months to emerge from a river. It’s not a very palatable thought, but it’s really common for people to drown and not be found for a while. And no, I don’t care what Peter Falding says. I’m far more inclined to think that he said too much too soon, bigger himself up about how wonderful his equipment was and how he would find her within hours, and then when he did, instead of admitting he got it wrong, he said that she obviously wasn’t in there and backed out.
When she’s found he’s going to look like a complete prat.