 In the third season finale, episode "The Day We Died", a gathering of ten Observers appeared on Liberty Island to watch and comment on the disappearance of Peter Bishop from existence.Later, he is ordered by his superior to ensure that Peter's status as nonexistent continues, and constructs a device to erase all lingering memories of Peter from Walter.However, at the last moment, he disobeys his orders and deactivates the device, allowing brief apparitions of Peter to appear to Walter and Olivia.