There's also the possibility that someone with power knows who it is, and is blocking the police from doing anything. Basically, a threat. Could be a Yakuza, could be a agreement, for some reason. Political reasons likely. Maybe they have shit on the chief or something, and the chief is blocking investigation. Who knows what is going on. Could really be many things.
I can easily image an analogy with Mexico, where narcos, police, and politicians all end up involved all that perturbing shit, and people disappearing is part of that politicking BS between the three powers.