That’s a really good point, and it is hard to reconcile.
I agree 100% that this wasn’t some “slick Hannibal Lecter” type and there was a massive element of luck in getting away with this. But also even with that in mind, it seems unfathomable to me that someone—no matter how bumbling—would stick around after a crime like that knowing there are likely to be people directly next door unless they had a very good reason for it.
So what are those scenarios?
1. They knew about the soundproofing, at least to some degree.
2. They had another objective at the house, such as finding something there.
3. Their hand injury was so bad that it HAD to be their first priority following the murders, and after nobody showed up by the time it was patched up they figured nobody heard anything.
I hadn’t considered scenario 3 until now, but the more I think about it the more it feels plausible.
Any other possibilities you all can think of?
That's a great point, yeah.
The sticking around is possibly the strangest choice he makes out of A LOT of strange choices. I mean it's quite possible he's highly disturbed or that his reasons for carrying out these murders wouldn't make sense to an average person. But he's not totally stupid, his actions prove that. 1) he patches himself up, seemingly understanding infection and hygiene. 2) he doesn't let himself get caught, even if he does run a high risk by hanging around after the murders. 3) he doesn't turn himself in and never pops up on police radar again. So, all of that suggests some clear self-preservation tendencies.
And we accept he understands self-preservation, he must have therefore understood risk. No matter how dumb or lucky the guy is, he had to have known that carrying out four murders and hanging around is a big risk. Especially with a house next door. So, to answer your question:
1. He knew about soundproofing but hadn't actually tested its capabilities. Because, without getting into spoilers, you can take it from me that it WOULDN'T have blocked out screaming or banging against walls. PLUS, even if he does want to rely on the soundproofing, how does he know nobody will phone the cops in the heat of the moment. Or a passer-by will see something through the window. Or someone will run out of the door in the middle of the attack. There are just so many things that can go wrong, that he would have had to have been MAJORLY confident if the soundproofing was his safety blanket. Or, as discussed, not smart. Also possible.
2.If he wanted something specific from the house, that would better explain why he's willing to accept all that risk. But here's the problem: no family members could identity anything missing except money. And as discussed in the podcast, I'm not buying money as his motive. So we'd have to be talking about something the family had that nobody else knew about or could fathom. That leaves a sexual motive, of course. I can't talk about that at this point but you can probably guess that for one reason or another, it hasn't solved the case for me.
3. Makes a lot of sense. We do know the blood loss was significant. That might well have sent him into shock, or made him extremely tired or compromised his decision-making (assuming that was in good shape to start with). However, the injury wasn't enough to stop him finishing the job after Mikio and Rei were dead. Or stop him from searching the house and filling a bathtub with water which he then crammed full of objects. Or going through their personal items. Or logging on to their ice cream. Or eating their melon. (Both with one hand). Or drinking their barley tea. He did rest on the couch so that could point to him being quite badly hurt. The blood tells us he can't have been feeling great. Especially when the adrenaline thins out. But his actions don't necessarily square with a badly-hurt man.
4. Given his actions are so illogical, I had always assumed there might be some kind of substance going on in there. Thing is, the blood and stool both reject the presence of drugs in his system.
5. The last possibility I can think of right now is timing. He had a train to catch. Or a plane. Or a curfew. Or he was meeting someone. Given the injury, he couldn't walk around at night. So, he figures he'll kill time in the house. As you say, if nobody has kicked up a fuss yet, he figures he's gotten away with it. The fact that he dresses up in the father's clothes seems to point to this. After all, if he walks out of the house at 1:30am, why bother changing at all? Why not just walk out in your own gear, it's not like the blood is going to show up so late at night. It seems to suggest he felt it was safer to lose them altogether -- was he anticipating being seen? An airport or associates or a family? I think it's quite possible he was manufacturing an alibi -- maybe not for police -- maybe for a girlfriend, even. Either way, if he comes home in the middle of the night, bleeding from a hand injury, that could create more problems for him than just staying in the house until daylight or whatever time he left.
