Reginald "Bunny" Whitby was Detective Ed Green's former bookie.
Background
At an unknown point, Bunny started frequenting a gambling joint and accepting bets, becoming a bookie. He also developed an addiction to cocaine, which made him unstable. In 2006, Detective Green started gambling as a coping method when his former partner, Lennie Briscoe, died and Bunny was his bookie. Green later introduced Bunny to another customer named April Lannen, and they started gambling together. Green eventually quit gambling when his losses started to pile up, but Bunny continued accepting bets from Lannen. Lannen eventually got so deep into the gambling that she started embezzling money from her job to help pay Bunny back. Bunny then started using Lannen to sexually service some of his friends to help pay off her debts. When Green found out, he went over to the club and assaulted Bunny, telling him to leave Lannen alone or he would charge him for pimping Lannen out. As a result, Lannen eventually paid off her debts and stopped placing bets with Bunny.
Burn Card
In 2008, when another of Bunny's clients, a real estate agent named John Singer, starts losing repeatedly to Bunny, Bunny goes looking for him at a bar and questions the owner, another small-time bookie, for information. The owner say he doesn't know anything, but Bunny beats him and empties out his pocket to help pay off the debt. When he does track him down, Singer promises to fix a basketball game he was refereeing part time to help close the debt. Singer does his best, but when he fails to deliver on his promise, Bunny tracks him down and shoots him once in the chest, killing him. Bunny later runs into Lannen outside the gambling club where he did business, and she tells him the police are looking for him and he needs to disappear. However, Bunny thinks she ratted him out and assaults her. However, Green approaches him from behind and shoots him in the back to save Lannen's life, killing Bunny.