Well, for starters it means he wasn’t lugging a dead body 350 metres. The start time and duration of the rape could easily match the screams SA heard. Stopped car 12:11, near pond/river 12:14, over in minutes 12:17, back in car 12:19.
I just think he had to deny being anywhere near that river because he knew that’s where she ended up.
Imagine his dismay when, having told the police he had sex with Libby on Oak Road, a witness came forward to report screaming near the pond and an alleged fleeing man. And again when Libby was found in the sea. And again when his semen was found in the post mortem.
His story changed each time the police had something new on him, and he only admitted things when he absolutely had to because there was evidence.