[Beldin]

I don't remember that case at all. Possibly because I'm not American.

Could you elaborate what would be a valid reason? From what you wrote, it sounds like someone started shooting after some kids said some things. I can see that as an argument for gun legislation, but not for installing microphones in public spaces.

[SilasX]

It would be the same issue if he simply assaulted them with his fists -- the recording would help to determine if he was being threatened.

You can look up the case on Wikipedia and elsewhere if you're curious:

https://en.wikipedia.org/wiki/1984_New_York_City_Subway_shoo...

Bottom line, it's really not hard to imagine that audio recording would help determine important facts of a case; this shouldn't be controversial in and of itself. The issue is the relative cost to personal liberty.