With the greatest of respect, I can't subscribe to your reasoning
It would only take someone in the adjacent building to look down as the neighbour entered JY's place and that's something that couldn't be undone and would place neighbour squarely in the frame. It's too risky and even those with average or less intelligence would appreciate that the risks would far outweigh whatever gains. There are flats to the rear, to the front, to the side. He would really be pushing the odds recklessly to expect that not one of those many residents - or a passer-by, or a visitor -- would see him
Had the killer dumped the belongings in a bin, or skip, or tossed them from the car anywhere along the route, it would have confounded investigators to at least the same degree as would placing them in JY's flat
If the belongings had been left with the body, the public, media and investigators would still have been confronted with a girl who'd been killed. If her belongings were nearby the body, it would have been speculated she'd been pulled from the street by persons unknown. This would have lessened suspicion upon residents of the flats and nearby residences. If the killer had for whatever reason chosen not to place the pizza and sock near the body, the task of investigators would have been as difficult as we've witnessed. And again, would not have thrown suspicion upon residents of the flats
The fact JY's keys, phone, coat and boots etc. were discovered within the flat, along with the half-consumed cider is what focused attention upon residents of the flats. If the killer had had the wit to dispose of those items along with the body, the search would have been away from the flats. By leaving those items within the flat, the killer virtually guaranteed he'd become a suspect, imo
The brother is white as driven snow. He is. He really, really is. Honestly. He is
