LINK TO COP SLANG LIST
Writing realistic dialogue for cops and bad guys can be a challenge for writers. How do you determine how they really talk? One way is to consult someone who works in law enforcement. The extensive list at this link can also help. Be forewarned some of the terms are rather profane so consider your audience.
Even the term "cop" is slang. While most police officers do not consider the term offensive, they don't refer to themselves as 'cops."