any person rising through the ranks of an urban police/corrections force is going to have "whispers"; every promotion is resented by someone, every decision makes enemies, and they talk and spread innuendo, and on and on it goes. unless you can find some high ranking monk who doubles as a high ranking police official. that leaves nominees to come from the political class or empty shirt beauracrats - which is likely where the nominee will come from now. either we will get a politician (Lieberman, Pataki, etc), or some Norm Mineta type person.
There's something about this kind of job that seems to attract a certain kind of person. If you go back and look at Kerik's career in law enforcement, you'll find some remarkable parallels to a phony who rose through the ranks in a similar manner right across the river in New Jersey -- Joseph Santiago. This was the guy who fabricated a career for himself as the New Jersey State Police Superintendent under Jim McGreevey, and was eventually fired after his name come up a number of times in Federal investigations of organized crime figures in New Jersey.