Continuity mistake: When Leela is found on the door step she has a bracelet on her wrist but in the next shot it is gone.
Continuity mistake: When Fry (Captain Yesterday) is falling after the gem, the clock is at 10:05. When he lands and we see the clock, it's 10:35.
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]