ja.m.wikipedia.org
So this is Japanese Wikipedia on Setagaya murders. Google translate works better if you cut/paste in pieces, the in bulk translation didn't work for me, for some reason.
Talk about the job they did.
I just have read it, and didn't know yet, and it is the information from Japanese newspapers of 2010, but apparently, the murderer's treatment of bodies PM may indicate he knew them? Since it is Wikipedia it is not information withheld by the police, but when I read it first, I wondered if the perp had indeed killed someone and buried in the desert before? And since he could not bury, he did what he did in this case.
Two types of sand, one, it seems, from Edwards base, another, in a pocket, from a local beach area where the victim's family stayed in the hotel 2 years prior?
Some connection to the skateboarders exists, and it seems to me that the police has some information about the perp's connection to California.
They have different sources of DNA.
Finally - i found the type of maternal mitogroup - ha! Greeks, Ashkenazi Jews, the Pyrinees, Siberia, some in Northern Africa, you name it. Not super uncommon although not the most common subclade within the hugest group. Full mito sequencing can be of huge value.
His sidewalking between the bodies, like the military would walk in the barracks, is of interest, but it seems typical for anyone with military training.
To me it seemed that it was some connection between the victim and the perp, and also, it appears that the perp is very angry with women. Maybe he doesn't like higher-pitched voices.
About the sounds. The intercom buzzing that the neighbor heard but the people in the adjacent house did not. Indeed strange that so little was heard by the relatives. The article says that An Irie and her family lived previously abroad for a while (and at that time the cram courses were held by Yasuko in the other house). (It would be of interest where they lived?) They obviously have been ruled out and it seems are sincerely grieving, though.
Having read this, JMO - the connection between the perpetrator and the victims might exist, although in an indirect way.