Mystery film is a sub-genre of the more general category of crime film and at times the thriller genre. It focuses on the efforts of the detective, private investigator or amateur sleuth to solve the mysterious circumstances of a crime by means of clues, investigation, and clever deduction. The plot often centers on the deductive ability, prowess, confidence, or diligence of the detective as they attempt to unravel the crime or situation by piecing together clues and circumstances, seeking evidence, interrogating witnesses, and tracking down a criminal. Suspense is often maintained as an important plot element. This can be done through the use of the soundtrack, camera angles, heavy shadows, and surprising plot twists. Alfred Hitchcock used all of these techniques, but would sometimes allow the audience in on a pending threat then draw out the moment for dramatic effect.