Citing the episode's grislier-than-usual content -- Molly Shannon playing a character brainwashing children into killing other children -- Fuller asked the network to pull the episode.
"Given the cultural climate right now in the U.S., I think we shouldn't air the episode in its entirety," Fuller told Variety. "I didn't want to have anyone come to the show and have a negative reaction."
"With this episode, it wasn’t about the graphic imagery or violence. It was the associations that came with the subject matter that I felt would inhibit the enjoyment of the overall episode," he said. "It was my own sensitivity."
Episode five will air in its place, and NBC says it will not cause any problems with continuity in the show. The show's freshman season will be one week shorter, with the finale now set for June 20 instead of June 27.
NBC said it will package clips of the unaired fourth episode and make them available online next week. The episode will air in its entirety overseas.
Earlier this week, ABC also announced it would switch up its broadcast schedule out of sensitivity to the Boston bombings, swapping April 22's planned episode of "Castle," in which Detective Kate Beckett steps on a pressure-sensitive bomb, tentatively swapping it with the April 29 episode.
"Hannibal" airs at 10 p.m. on Thursdays.