Yes, Dianne did rather give the game away, though they cut her next line which was "and the suspect is Supervisor Dan White". Having had this warning of the deaths, though, my friend said she worked out who the killer was fairly quickly.

I wondered if the woman behind us had forgotten the set-up by the time we got there, because she seemed so shaken when it actually happened (both times). Probably she was just so caught up in the story that the shootings retained their shock value even with foreknowledge.