Thank you for the information about the difference between manslaughter and murder.
I think even if charged with murder PR will try and claim manslaughter .
I can see the police wanting to try and get every shred of evidence they can to make their case 100% watertight.
I'm another one over here in the corner who thinks that the spectre of manslaughter will haunt this prosecution, if it comes to court. The CPS would have to prove intent to kill and all that they have got at the moment is that he seems to have inveigled her into his car presumably with some sort of sexual intent, and even that is based on the assumption that the police have more of the "spidercam" footage than was released, because otherwise the defence will make hay with the bit that we've all seen. Then I would imagine that the accused's first line of defence would be that she got out of the car afterwards, or escaped during, the sexual assault and he never saw her again. The fallback position, if that is disproved in some way, would be that he'd claim the incident got out of hand and she suffered fatal harm, and he would therefore opt for a guilty plea to manslaughter which he would hope would bring a lesser sentence.
I suppose the police and CPS have the CCTV of him going in to the playing fields, and it could be that they have additional evidence from Greybeard the Good Samaritan which they are keeping up their sleeve until it comes to disclosure time, surrounding the events around the bench. He also admitted to a family member (assuming the bloke in custody is the right one) that he'd picked up "a crying girl", and given her a lift.
Other than that, there is the forensic evidence from Libby's body, which may also provide a cause of death and an indication of the time she was in the water, and that's about it. The fact that they haven't moved to bring charges yet could mean that they are waiting for more tests or that they haven't got enough, and that's that. Even if they found DNA the defence would presumably claim it was transferred during her time in his car.
I have looked at the Croda CCTV and to be honest the bloke on a bike could just be a fast food worker going home or a shift worker headed in to work - we're a 24 hour society these days - I think there's a Royal Mail facility somewhere in the area that would be 24/7. The jogger? Well, could be just a jogger. There is a type of jogging where you alternate walking and running called, unbelievably, a "fartlek". The guy could just be fartlekking. And the couple, if they are indeed a couple, could have been on their way back from a tryst of their own, which is why they haven't come forward.
It's quite a depressing vista, all told. What the case needs is something to put the accused and Libby together in the park after the fatal "event" if indeed there was one. As others have pointed out, she may even have fallen into the river in her attempt to escape.
At the moment, unless there is something we don't know, which the CPS and police are keeping quiet, it's looking like all he would have to do is sit there parroting, in questioning, "no comment".