How to write a dialogue between a detective and his/her companion/assistant, explaining why the discovery of a book of poems next to the dead body of the victim, could be a vital clue.
It would be best to look at models from classic detective novels and short stories. I would suggest examples that represent two different types of detective. You could start with Sherlock Holmes, the gentleman consulting detective, who relies on intellectual prowess and uncanny powers of observation. Examine any of his conversations between Doctor Watson or Inspector Lestrad. You could also watch an episode of the television series Elementary, which imagines Holmes as a consulting detective in modern day New York City, to glean a useful example of interaction between Holmes and a variety of characters he uses as a sounding board for his analysis of a crime scene.
The second would represent the hard-boiled private investigator. He usually relies on a "Girl Friday" who acts as his receptionist. Unlike Holmes, this type of detective relies more on instinct than intellect. He will examine hunches and treat them on the same level as solid deductive reasoning. A good example for this type is Sam Spade in The Maltese Falcon. His secretary is Effie Perine, and Sam relies on her women's intuition especially when a case centers on a femme fatale (dangerous woman).