Castle (2009)

A best-selling mystery novelist works with the NYPD to find a killer who has been recreating crime scenes from his novels.

Famous mystery novelist Richard Castle gets permission from the mayor of New York to let him tag along with one of the police department’s female homicide detectives for research and to break his writer’s block. He creates a character based on NYPD Detective Kate Becket as he follows her along to all of her crime scenes. 
His knowledge of crime becomes useful and he becomes involved in actually solving the cases.