Sorry if this has been posted before, if the jury were to see the flat basically as it was found as a crime scene, the curtains in the living room are closed.
The bedrooms very sheer curtains were closed but it appears the pull down blind behind is almost up and you could see through those curtains at night from outside if close enough, especially through the space where the curtains meet in the middle.
The venetian type kitchen blinds in the kitchen are open but Jo could have opened these in a darkened kitchen to check for the cat, a noise, a knock at the door or in response to the security light coming on.
Since VT was familiar with the cat and played with it often, it must have been regularly out and about and as Cherwell said the cat could be involved in some way.
He could well have used it as a decoy or some pretence for Jo to open the door. A sensitive security light will respond even to a cat passing or at the doorstep.
The timing of Jo returning home and the screams go some way in showing that he could have entered or pushed in with the intent to attack and kill (or was already in).
But no matter what his defence, imo nothing is going to take away the state of Jos body and the time it took for her to die. He could have stopped at any time but he continued until she had expired. imo that alone will be enough to convict him of murder.
