I think he was either killing time, yes, or he simply needed the time he needed to feel well enough to walk out. And as comments below and several times in the thread, yes he used both first aid products and the mother's sanitary pads to stem the bloodflow. The Chief said several times, he lost a "significant" amount of blood in the house. And yet he persisted with the killings. That tells me, there's no effing way this was a robbery. A robbery's motive is financial.
The injuries seem to be to both hands, not just the right. It seems as if he switched the knife to his left hand after hurting the right one. Which explains why there is blood in both gloves. I believe the slices and cutting to the gloves gives the TMPD a steer on HOW he was injured and also how much was in the gloves / how much blood was left in the house. It's not 100% certain but I would bet my life that he is carrying scars today at least to his hand hand/wrist.
I haven't heard about a mailman / seeing a light on in the house. As I say, the ONLY CERTAIN time stamp is 10:38pm to 1:23am. There are a few 'witness statements' on the night but none of them sound that credible. Supposedly, Yasuko herself complained about 'a car parking too close' to the house in the days before the murder. This is the one I'm most likely to believe (and incidentally, I believe the killer had access to a car).
As to whether or not the killer used public transport to escape. I find this almost impossible to believe. Sunrise on December 31st in Tokyo is somewhere around 06:50am. The first train of the day in Tokyo is around 5am. So even well before sunrise, there are going to be people on those trains and it's a city of 40 million people. I find it extremely hard to believe that NOBODY saw a young man, with no jacket (that we know of, Mikio had none missing that we know of) and extensive hand injuries / bandaged up with Yasuko's sanitary pads? Not one? On a day when many people would be travelling early to see family, leave town etc. For nobody to remember him, especially when the news breaks shortly after? I suppose it's possible but the killer would need miraculous luck. For me, it is massively more likely he either left on foot meaning he was almost certainly local or had somewhere to stay locally for a short time before getting the eff out before the heat rolls in. Or he left by bike but his hands were shredded so that would probably have been very uncomfortable at the very least. OR, for my theory connecting him to Yokota to hold true, most likely he would have had a car. Which both solves the journey to Yokota, some 30-40 minutes away, and explains how nobody saw him at all.
But, a car means at least 18. You can drive a small motorbike at 16 in Japan, and a car, only at 18.
Now assuming he is from Yokota base and drives a car, where does it put us?
First, he is not that impaired, mentally or otherwise. Metropolitan Tokyo, in 2000 was a tad less than 35 million people. I had to recheck it to believe. Left-side driving. Even with their wonderful subway, I would never risk to drive a car in Tokyo. If the perp was driving a car and young, this mere fact throws a lot of assumptions out of the window. He can’t be slow, he can’t even be klutzy, he may be slightly nerdish but pretty with it, physically. The police said, living a student life. So maybe, he was attending some college taking Japanese classes. And parents bought him a car, because, independence, why not.
BTW, is there any cultural difference between Japan as compared to, say, South Korea and US in terms of buying a child his first car? In the US, it is almost a must in school. Would Japan be more modest in their approach?
I wonder if he, indeed, had a car but lived somewhere closer, in a dorm? And used the car to get around. He could have sneaked out of a dorm but drove the car to get back to the base because no way would one return back to the dorm wounded.
Plus, imagine he uses the car to get back to the base. He is still supposed to show some documents, it is a base.
I think neither of these things happened. I think he came out, called from a phone booth to one of the parents and they picked him up.
Or, if he is not from the base, a local but in the same circumstances, he probably called his family, too, and the same happened.
Or: he is not a 15 or 18. He is an adult, close to 30, and has been driving around and living an adult life. He might be a local who slipped through the net. Or if he is from a base, he might be the husband of a woman serving there. Why not?