I showed him a particular immigration document issued to me that he is not, strictly speaking, allowed to ask for prior to starting a custodial interrogation. He then started second guessing Immigration's decision to offer me a visa.

That was good news, since it convinced a colleague he was overstepping his authority. I was released 5 minutes later, with an admonition to lock up my bike properly to avoid the scourge of foreign bike thieves plaguing Ogaki.

If you look at the criminal justice system as having some amount of diagnostic sensitivity at each stage in the process (having both false positives and false negatives as all systems do), then our comparatively lower conviction rate means that (assuming end-of-the-day-justice is equal), we should be even more willing to waste people's time developing cases that have no merit (because more of the diagnostic sensitivity is in the trial/conviction stage). So it's not unreasonable to assume it's easier to get a wiretap in the US than it is in Japan -- another explanation is that Japan is substantially more likely to have false negatives (as implied elsewhere -- but the false negative rate for many crimes in the US is quite high, as roughly half of all murders go unsolved). Could also be that the diagnostic sensitivity is extremely bumpy in America or Japan (read: basically one or two steps / people get an extremely high share of the criminal justice discretion).