Amazon Women in the Mood - S3-E5
Easter egg: On the episode menu, there will be a choice of the usual "Play", "Special features", etc. On the left of these options you will see a picture from this episode. Press left and it will be highlighted. If you then press enter you will go onto an easter egg showing the rejected gags beneath "Futurama" in the opening credits.
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]