One other thing that caught my attention is who wears white to commit this type of crime? White is the easiest stained color. Things like blood, dirt, food and other incriminating materials would be very noticeable against it and could draw attention in public, which is something perp supposedly doesn’t want to do. And yet the perp still left himself vulnerable to the possibility that he would need a change a clothes? Even the bag is too light in color. Wouldn’t it have been better and more advantageous for him to blend in both inside and outside the house in the dark by choosing a wardrobe entirely black or dark in color? Seems like an amateur move on his part IMO.
RSBM: In terms of killing, we can assume he is very much an amateur. In terms of his record in Japan, that's a given. He had never offended (or been caught offending in a way that left fingerprints / DNA). This is just guesswork by me but: we can debate the killer's IQ all day long. For anyone thinking he was a dummy, which is wholly reasonable, surely he's not going to be stupid enough to realise that a white shirt is a bad idea when stabbing several people to death. This supposes two things. 1) That he went there to stab. 2) That he went there to stab, knowing he would be taking off his jacket -- which was dark in colour.
My own view is that the murderer was veering towards the intelligent side, even if clearly not a seasoned killer. He was a determined one though, as evidenced through cutting himself quite badly while attacking Mikio but carrying on. As you can see in FACELESS, the experts in burglary find that astonishing. A man there to rob them is not going to start by killing a sleeping child and is almost going to certainly flee upon discovery. Let alone go upstairs to finish off two people who likely hadn't seen his face by using his weak hand after slicing his right hand open.
Why does his intelligence matter? Well, for me, it's more his decision-making. I think it's entirely possible he didn't plan on getting that white shirt dirty. But once he realised he'd bled everywhere and that the hallway was particularly narrow / he was likely sweating and flooded with adrenaline or anger, he figured in for a penny, in for a pound. I would guess he also didn't plan to spend so long in the house. Perhaps, he thought he could simply dispose of his bloodied jacket afterwards. Now, it's possible he had clothes outside somewhere. But then why steal Mikio's afterwards? A sweater wouldn't be enough for warmth / not stand out. (That, in a minor way, again points to a car to me). I think he did enter that house with a plan, but the plan went south. He still kept his calm, and pivoted accordingly. FWIW, that doesn't smack of a madman to me, or a bumbling idiot who simply got lucky. While he is likely to be mentally unsound at the very least, and while he definitely got lucky, I do think he was smart enough to update his plan during the murders / and after them. JMO.
When he attacks Yasuko and Niina his attack seems even more vicious and frenzied, especially with the numerous wounds against their head, face and chest. But why? Not to be grotesque but he could have just targeted certain areas of the chest and abdomen only once or twice to cause fatal damage to his victim’s organs and blood vessels.
I've speculated on this 'disparity' in violence between the Yasuko + Niina / Mikio + Rei many times. In short, I'm not sure I buy there being such a difference when Mikio had his fingertips sliced off, and a very sharp knife plunged into his brain and heart several times. But I do think it possibly illuminates the fact that he had some idea of who might be in the house. How does he know they didn't have 8 kids? Or Uncle Takehiro wasn't staying? To me, he let's himself go with Niina and Yasuko, yes. But that's either because of *them* / because the plan hasn't gone to plan / he's hurt and he's scared and he's enraged that he feels he might be caught. Just spit-balling here.
If the question is: why did he engage in such brutal overkill, then that's the $64k question, basically. Why them? My guess is that he had underlying rage for reason X. And he picked the Miyazawa family for reason Y.
Why use more of his strength, time and adrenaline when part of his goal also includes not only looking for something but now also treating his bleeding wounds?
As above but we don't *know* that he was looking for anything. He could have been staging the scene. He could have been disrespecting their household. He could have been simply curious.
Was he letting his rage out or was he starting to feel overwhelmed, frustrated, ashamed or panicked at the realization that his fantasy did not in fact match reality as he carried it out and he was at risk of getting caught if he didn’t finish the horror/atrocities he has started.
My feeling is that you're on the money here.
Also, what happened to his hands or how were they affected after committing the murders? Did he develop any nerve damage or loss of function of his fingers or coordinating them altogether overall? Did any possible classmates, girlfriends, friends, partners, colleagues, teammates or family ask about the scars? Was he still able to type? Could he write with a pen the same way as before? Could he still use the same equipment at work, carry school books with the use hands and arms at school or pass money from his person to another? How was he with sports and dressing himself without help?
An injury to his wrist / little finger on the right hand (left hand injuries are unclear) would likely allow him to live out his life with such movements unaffected. I'm not a doctor but I would imagine the knife would've had to go pretty deep to lead to impaired movements for life? Scars on the killer, however, according to the TMPD forensic folks, are "almost certain." I think there's no way he lives out the next weeks without anyone noticing his injuries. Unless he's a mountain hermit, of course. But who's doing that at 15? Who's also capable of visiting an American military base on the other side of the world and living off the grid, beyond the grasp of the TMPD since childhood? Maybe he IS Jason Bourne. Or, more likely, he had people around him who knew what he'd done and chose to ignore it. Or believed some story he concocted.
Did a doctor or parent ask questions about why happened? How did he keep his wounds from getting infected or causing too much blood loss?
Without getting into too much detail, my theory includes access to medical attention in a way that would be untraceable to the TMPD.
I do feel, IMO, someone likely noticed something different about the perp, even if they did only subconsciously, because of a physical change or symptom caused by his injuries that would have stood out out and likely led to questions or concern from them.
JMO/speculation
I agree. So the next question is: did they know about the murders and say nothing? Or did they simply not know about the murders and buy whatever BS story the killer offered up? OR, did he outright tell them what he did and they, for whatever reason, chose their love for him over possibly handing him over to the hangman? Love or complicity or fear? En fin, choose your own version.