At UWisc, they won't let anyone but a forensic pathologist and his asistants do any autopsies that may lead to a criminal case...this is b/c anyone present at the autopsy could be called to testify, and if the witness is not an expert it may hurt the case.
However, med students, etc. can ask to watch non-forensic autopsies (which is unfortunate since the forensic ones are the most interesting). I think you have to have a legitimate reason in observing one though (med student, nurse, paramedic, etc. is my guess)---so Joe Schmoe can't just wander in off the street and get to watch an autopsy.