Gothamist has the best roundup of the different versions of the story of Fred, the undercover cat for the Brooklyn DA's office. It's a fluff story (pun most definitely intended) about a serious crime: a Brooklyn man who had little veterinary training and certainly was no doctor posed as a veterinarian and made house calls for about seven years. He got caught when one of his clients thought his sick and wounded dog hadn't been properly cared for and went to the police. Fred the cat, a former stray, got involved in the sting operation that finally nabbed the guy. Now he's a guest of the DA's office and available for future detective work. Make sure to check the links to the NY Times' story and photos. I think they've got the best version.
I'd like to see more of Fred. I think he could investigate the disappearance of many catnip mice in my apartment over the years.