Most people wouldn't have followed what was said in court: they followed what the newspapers reported about what was said in court, much of which was sensationalised in order to get people to buy the papers!
Of course there is no evidence that VT went to ASDA with Joanna's body in the boot of his car, and of course Mr Lickley knew that.
IMO, somebody who can go shopping with a body in the boot of his car, AND look perfectly calm on CCTV while he is shopping, has to be an experienced killer, not someone who has just committed his first murder. No evidence has ever been produced to suggest that VT had killed before---------------------.
While I agree with your post, the last paragraph, try looking at it like this:
You're a first time murderer, this awful fact is maybe trying to get into your brain. Maybe you deny it, maybe you accept it. You are running on fright, panic, auto-pilot, adrenalin and whatever, so what appears idiotic to us, like going to ASDA with Joanna in the boot, just doesn't register in the murderer's brain. I mean if you've just murdered someone going to ASDA maybe would be quite normal to that brain at that moment.
I don't know, I've never killed anyone, but I did many decades ago see a friend walking down the road, she looked quite normal, apart from the fact that I had to say her name about three times before she responded. She was so worried and inside her head that she said afterwards that she couldn't even remember meeting me. Turned out her young daughter was last seen being given a hand into a strange car. Ended up that mum wasn't told that daughter's friend's mother had got a new car. Makes you think, even small things like changing your car things you don't think twice about, can cause real fright to another person.
Well these are just my thoughts mrswah on how a person might react having killed for the first time. I think logic as we know it can be thrown out of the window.