Former Iberia Parish Sheriff Sid Hebert was supposed to play the Sheriff, but he was later replaced by Gary Grubbs. As a sort of consolation, numerous "Re-Elect Sid Hebert" signs were placed in the Sheriff's office, and other places in the film.
Indirectly regarded as a goof: While it is true that John Bell Hood lost his right leg at Chickamauga, his soldiers chipped in and bought him a fine prosthetic leg of cork, imported from France. He was a Lieutenant General for Joe Johnston, then from August, 1864 until January, 1865, a full General commanding the Army of Tennessee.
When General Hood advised Dave to pay attention to what Adonis Brown told him. (That the killer was protected, either by the mob or the cops.) Dave took that and doggedly went after the mobster Balboni. But Dave would have found the killer much faster if he'd gone after those associated with the police. This is true to the book.