This video lecture was actually floating around a few months ago, but I just got around to watching it (well, actually listening to it) today.  It's by a law professor and former defense attorney, as well as a Virginia Beach Police Officer.  It's about 45 minutes long, and the general conclusion from both is that you should never talk to a police officer.  Even if you're completely innocent.  Just don't do it.  Nothing good can come of it.  But I'll let you watch and decide: