It's possible, yes. Though whoever's house he went to, hasn't either not suspected him in 24 years or has kept their silence for that long. If the latter, that would suggest a permanent relationship to me, such parents. RE: the reporting, I can't say for sure in terms of TV but speaking about newspapers, the first English-language piece is January 1st in The Japan Times. So, it's fair to conclude this news broke the very first morning of the 31st. In that reporting, it explicitly says, police on Sunday said... So, that's the day after. There was a press conference. It's a slow news period at the best of times according to the journalists in Tokyo I spoke with, so something like this, you can imagine. HOWEVER, all that said, there are places where people may not have been keeping up with the news. Rural areas, for instance. A US military base. How many were avid readers of The Japan Times? How much directly linkable information was carried in those early articles which would not only impel such a person to 'rat on' their son or friend or boyfriend etc but that would have been enough for them to make the realisation in the first place?
Yes, all possible. Or it's simply your son. So your choice is, give him up and he will potentially be executed by the State, or keep silent.
Japan definitely has a witness protection programme. I am not aware of this relating to the Miyazawa case, however. I agree that there is almost certainly at least one person who knows, at a minimum, that the killer showed up with a fairly bad injury directly after the murders. My feeling is, however, that such a person doesn't necessarily still have to be in Japan.