She keeps begging me to tell her who the killer is. At what point did you figure it out? SPOILERS
I knew before I ever watched the series. That's because my dumb friend showed me Fire Walk With Me thinking it was the pilot. (The pilot was hard to get in those days.) So I went into the series knowing every excruciating detail of Laura Palmer's death and with a very bleak outlook on the inhabitants of Twin Peaks.
I still love the series, but I wish I had been able to experience the mystery like everyone else.