Continuity mistake: During the chase after the concert we see Beck's tour bus in the mirror of the Combi. The word Beck in the front of the bus is the right way around. It should be reversed. (It is the right way around in other shots). (00:19:30)
Continuity mistake: When Cylon and Garfunkel are singing "Scarborough Fair" note that when you see them from the front there is one microphone, but when viewed from behind there are two.
Answer: You are thinking about episode 20 of series 2 - "Anthology of Interest I". She technically never kills anyone, but in the episode she ask a "What if machine" (one of the Professor's inventions) what would happen if she was more impulsive. The machine then shows the more impulsive Leela killing off the Professor to get the money from his will and thereafter killing Hermes, Bender, Scruffy, Cubert, Nibler, Amy and Zoidberg to cover it up. Finally she does something really impulsive with Fry.
Andreas[DK]