Newthoughts, thank you for your long and lucid analysis. That would certainly in my opinion be overwhelmingly the most likely explanation. You do however state at the end that it was PW on the balance of probabilities, which I think it's hard to disagree with, and which of course is sufficient for a civil case, but the jury will have to find it beyond reasonable doubt.
I think it will all come down to the the evidence of Mr Alford and the Claremont witnesses, and as to how certain or not they were. If Mr Alford said the man absolutely definitely had dark not light jeans on, or for example was skinny, it can't have been PW he saw. If he said the man was some way off, he didn't get that clear a view, he thought the jeans were dark but could be mistaken, it would be easy to simply dismiss his evidence. I am a bit surprised these witnesses weren't in the box longer, so maybe both sides figured they added little either way. Also presumably the prosecution knew what Mr Alford was going to say, so if he was going to describe with total certainty a man who couldn't have been PW would they have proceeded with a murder charge? Again we've only heard a sample of this. I would imagine the jury have long since concluded PW would say anything to help his case, thus they are disinclined to believe anything he has said that does help it. I think as far as his defence is concerned his evidence is a total write off.
Also I guess not impossible PW who from other footage was the owner of a camo style jacket and appeared to be wearing it when at Tesco that night, could have taken it off and have had a more bomber style top underneath.
As to how Libby got to the river I believe any suggestion she wandered into the park after PW left to be ludicrous. Yes she was drunk and emotionally upset but I see no evidence that she was incapable of any rational thought. Yes she was unsteady on her feet but the earlier footage shows her successfully crossing a main road and avoiding the traffic, and I see no evidence to suggest she was so out of it she had no idea where she was. I do wonder if the defence will suggest suicide, which I consider even more preposterous. I suspect they won't as I don't think it will play well with the jury.
Someone just asked could the rape have occurred post death, and I wouldn't by any means discount that.
I have wondered how PW (or the random stranger if not PW) got poor Libby maybe 200m into the park before anyone heard any screams. Maybe she ran and he chased? Maybe she fell asleep and he carried her? Any thoughts?