This is a pretty good article about something that happened a few months ago. Might be a repost, the original event happened before I was a member here.
http://www.salon.com/news/feature/2005/09/26/rave/
You have to deal with the salon.com BS "free pass" unless you're a member. Just mute the sound and look at something else while you wait. If the video link there gets killed, there are more here of you scroll down:
http://www.music-versus-guns.org/mamboserver/component/option,com_remository/Itemid,31/func,select/id,2/
The above site was constructed by the event organizers. The salon article is a good read that condenses the issues nicely. Regardless of your opinions of raves and ravers, the police overdid this by quite a bit. The guy with spare mags clipped together is a hoot.