I have been tormented by the central paradox of this murder and I have now devised a (partially) new hypothesis to attempt to explain it. Here goes.
Quite a few contributors seem convinced that the killer decided to remove the body in order to distract attention from the flat because he is someone closely associated with the flat or its immediate vicinity.
Obvious as this seems at first sight, this explanation suffers from an enormous difficulty when the killer carefully leaves in the flat his victim’s personal effects including keys, mobile phone, coat, bag and footwear. He offers us in due course a corpse which even lacks one sock. He knows we shall conclude that Joanna did not voluntarily leave her flat without these things and therefore probably was killed in the flat, in which case he might as well have left the body there too.
Two hypotheses have been advanced to explain this paradox :
1. Joanna before getting home, got into a car with someone else and was killed in it. The killer then took her effects to the flat to draw attention to the flat and thus away from the place where she really died. I don’t like this unless there were two people in the car or one very strong person and even then the advantages to the killer of taking the personal effects back to the flat seem hardly sufficient to outweigh the danger of being seen there.
2. While removing the body, the killer accidentally let the flat door slam shut and, not having other keys than those in Joanna’s bag inside, could not get back in to complete his original plan to remove the effects as well. Rossetti will allow me to be sceptical of this idea, which does not square with the picture I have formed of the killer – definitely not a man who wrecks his plans by accidentally slamming doors.
My suggestion is that the killer left Joanna’s personal effects in the flat in order to produce the one and only effect that could have : to draw attention very firmly towards the flat, and away from anywhere else.
Why then did he not leave the body there too ? I suggest because (a) Joanna did not die in the flat and the killer doesn’t like lugging corpses around more than necessary, (b) he didn’t want to run the risk of its being discovered too soon.
In this hypothesis, the killer wants the police to think that Jo was killed at home, but he also wants to leave as vague as possible the time and if possible the date when that occurred.
The story is roughly this. After Joanna arrives home on the Friday night, she is invited (for instance by a close neighbour) to have a glass of Christmas sherry with him. She accepts and goes to his place, wearing shoes on her feet and taking her bag, but leaving in the flat her pizza which she was getting ready to eat.
The neighbour knows Joanna and knows that Greg is away for the weekend. He does not know that Joanna has been recorded this evening on CCTV and he does not know that she has a till receipt in her handbag. Neither does he know that she made a call and sent a text after leaving her office party.
I imagine him attacking and strangling Jo, in his own home, a little after 9 p.m. on the Friday evening. Once the deed is done, as a close neighbour, and having obviously no genuine alibi for the time when he is committing the murder, he fears that he will be interrogated and suspected. He wonders what to do to divert suspicion from himself. He is perhaps not strong enough to lug the body very far. He thinks of dumping it straight away with all the personal effects at a safe distance, but he realises that it is likely to be found soon and that the spotlight will be back on him.
It occurs to him that the first person the police usually suspect is the spouse. Greg won’t do, as he is away for the week-end, but if the killer can succeed in fudging the timeline sufficiently, Greg might be suspected nevertheless. Failing that, the likeliest possibility to take the heat off himself would be for the police to believe that Joanna was killed in her own flat by an unknown chance intruder.
The killer therefore takes Joanna’s effects back to her flat to give the impression that she was attacked there. Seeing her pizza, he removes it, to leave the timeline vague as to her meals. Then he has a stroke of genius: he ostentatiously scrubs an area of the floor with powerful bleach, so that the next entrant into the flat cannot fail to notice. This will infallibly give the impression of a “forensically aware” criminal cleaning up after a murder. This was what convinced the police and family that it was a murder even before there was a body. It was meant to. This was what the Yeates parents saw but were not allowed to reveal.
Finally the killer leaves the flat and returns home where he loads the body into a tarp and takes it to a place of intermediate storage. After Greg is safely back home, he will dump it at some neutral spot he knows for timely discovery that will leave the police unable to determine a very exact time of death.
The rest of the story we know.
How am I doing ? Obviously quite a few variations along the same lines are possible.