Continuity mistake: When Bender and Flexo are fighting, Leela fires a shot at the roof and some bulbs fall down. The bulb's positions change between the shots. (00:18:25)
Continuity mistake: When they are looking for the stolen atomic tiara, Fry is looking through Leela's drawers. At first the panty on top is pink. When it cuts it's blue, then pink again later in the scene. (00:14:50)
Continuity mistake: As Fry is looking for the atomic tiara he's in Leela's room. Before he goes through the drawers there are three of them, but when it cuts there are two drawers. (00:14:50)
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]