Dark theory about the White Rabbit?
What if he is actually a psychiatric or other kind of doctor in the Darkwoods Penitentiary and an insider man of Starkweather. He organized the Smileys to take over the whole prison and Starkweather gave his orders via him. The doctor is dressed in the rabbit costume because in that way the lunatics don't see him as a killable stranger, but rather as a friendly good willed figure. As a doctor, he knows every one of his patients and how to make deals with them and how to trigger them to hunt for Cash(for example he told Smiley 1 that a bald guy in a blue t-shirt will come, he is the one who stole his shoes). In the meantime Starkweather and Ramirez don't go to the Smileys personally, they just talk to them via a radio and the Smileys think Starkweather is a god-like person who talks from the sky.
The rabbit seems surprisingly sane when Cash goes after him, so he is not as lunatic as the gang members.
If he really is a doctor who sweared for protecting sick people, it is very disgusting and horrific that he made his patients to kill people and die at the end.