No listen this is not at all completely esoteric....the Amanda Knox trail(s).
You are an American, you are in a foreign country where you don't really understand the law or the language. You are approached....something has been found...someone has been hurt....where have you been...can we have a swab....
What exactly are your rights? At what point can you ask for legal assistance?
In some countries you have no rights. In two that I know of, China and Belarus, you don't even have the right to know what the law is. (Hey, I was doing a survey of the Belarus National Library and I asked my guide, the International Materials Librarian, why certain copies of the secondary Official Gazette were missing from the shelf, their volume numbers skipped. She explained. That may be all you need to know about Alexander Lukashenko.
Abroad, as in the USA and the UK, "Nul n'est censé ignorer la loi": Ignorance of the law is no excuse. Even when the "law is an ass".
My advice: if relevant "just pay the man the $2"
http://www.imdb.com/title/tt0697156/I could list many anecdotes from life. Here's one. One is aboard a tram in Warsaw and the inspector declares that you have an invalid ticket. A £20 fine. Of course if you don't insist on a receipt, then £10 will do. (I was reminded of that story today when the bus inspector checked my Freedom Pass on the 137 bus. He didn't even bother to swipe it on his machine, they never do for those passes.)
The point of a tourist guidebook is to save you from pitfalls and scams. I was at Syntagma Square waiting for a bus to the airport when some local guy, who claimed to have lived many years in Manchester, stopped me and picked a friendly argument (about the US intervention in Serbia, a current issue, although it could have been everything). I was on the point of accepting his invitation to go to a bar for a beer when I remembered something: that's an old scam at that square, where a clutch of pretty girls will show up, the bartender will serve them, and you have to pay or go to jail.