What I know about Japan from reading Japanese crime fiction

• 'Great detective' is a recognised profession in Japan. The career path is not really clear, but it's a wonderful position if you can get it. The police allow you access to everything and everyone. They'll investigate what you tell them to and ignore what you want ignored.  You can conceal crucial evidence from them if you like. They'll understand.  And everyone calls you 'Sensei'.
• Japanese architecture is said to be unsuited to the locked room mystery.  This must be because Japanese houses are riddled with secret passages.  Sometimes the secret passages have secret passages in them.  These in turn may lead to massive unexplored cavern systems (and via those to the secret passages of your neighbours' villas).
• Everything you need to know to solve a crime in Japan is available in a newspaper.  Libel and privacy laws seem to be fairly toothless and a police officer in the presence of a journalist feels compelled to give out every detail of the case. If the chief suspect has a perfect alibi, millions of Japanese newspaper readers can still consider every detail of the suspect's movements, motives and actions over breakfast.
• Japanese police do not seem very result oriented.  They have an uneasy feeling that they're cheating, doing it the easy way, if they're not doggedly and painstakingly pursuing an apparently hopeless line of enquiry, the more man hours the better.  If the case hasn't involved, say, finding all the bookshop receipts from all the rubbish bins in central Kyoto, in the hope of discovering what the old man on the 5:30 to Osaka had been reading, well they might catch the killer, but did that really count? Japanese policework, perhaps, is not about catching criminals, but more a kind of Buddhist pursuit of enlightenment, like writing haikus or calligraphy. After two months contemplating the national railway timetable, the detective achieves inner peace.  If all he wanted was to find the murderer, he could have read a newspaper - those guys know everything.