Of particular note is Holly Hunter's performance as Inspector Monahan. In a movie that is basically a crime procedural, Hunter finds moments to flesh out Monahan and suggest a long history for the character. Take her first major scene. Monahan is walking through a house in which a murder has been committed, taking in the details of the scene, all while putting on a chipper smile and speaking with a gentle mother-like whisper whenever she comes across one of her fellow officers.
Very quickly, it becomes apparent that her gentle demeanor masks a tough interior as she gently interrogates the officer who first arrived on the scene. She picks up on the fact that he is withholding information through his subtle word choice and keeps questioning him until she finds out what she wants to know.
I don't know if this moment was part of the script or something Hunter came up with while developing the character, but what is apparent is that it is a choice made by the character for a reason. Maybe as a female detective she has learned that this is the best approach for coaxing information out of people. Maybe as a confident individual who has earned the respect of her peers, she doesn't feel the need to waltz into a crime scene and start busting balls.
Both of these could be true along with a few other possibilities. The important thing is that a scene that could have been just a routine exercise in exposition becomes a small character study. It is moments like these that make Copycat a cut above the rest.