Here are some terms to use in your mystery novels to make yourself sound like a detective.
Accessory — A person who assists in a crime
Alibi — An excuse used by an accused person to prove he or she wasn’t at the scene of the crime
Breakthrough — A big discovery in an investigation
Capital Murder — A murder that can be punishable by death
Case File — A collection of documents pertaining to a specific investigation
Deduce — Logical reasoning and thinking to infer information
Evidence — Clues to help solve a crime; can be a statement, fact, or object
Felony — A crime punishable by either death or confinement in a state correctional facility
Fugitive — A person who escapes or evades arrest or imprisonment
Homicide — The killing of a human being by another human being
Interrogate — To ask questions and get information from people about a crime
Motive — The reason a person does what he/she does
Parole — Allowing a prisoner to serve the remainder of their time outside of prison
Perpetrator — Someone guilty of a crime
Red Herring — A false clue to throw investigators off track
Suspect — Someone who might have committed a crime
Victim — A person harmed by a crime
Warrant — A written order directing someone to do something
Witness — A person who saw something related to a crime
Of course there are many other vocabulary terms to use when it comes to writing a mystery novel. This is the most I could think of that I knew exactly what they were.
I hope this helps!