Street talk?

As an avid viewer of true crime programs, one of the aspects that strikes me most is how inarticulate most detectives and police officers are. More often than not they have no skill with the English language, always say "lay" when it should be "lie", frequently makes statements like "should have went" or  "if I would have known" and dozens of other illiterate regionalisms. Is this a problem? Not necesssarily. Most of these guys are good law enforcers, good detectives, dogged, determined and devoted to catching criminals. Still it would be comforting if they could also speak English, if you got the sense that they went to college before pursuing a life of crime fighting.