A mug book is a collection of mug shots, which are photographs of criminals taken at their arrest. They must be carefully constructed with similar pictures together to avoid prejudicing a witness. The purpose of the mug book is to narrow down the possible suspects, and it is not used to convict criminals.
Mug books are often used before an arrest, similar to how a physical lineup used after an arrest. Law enforcement officials keep mug books on file. When a crime occurs, officials frequently take six or more similar criminal photographs from a mug book and mount them on a poster board to use as a photo spread.
Officials present the photo spread to individual witnesses. The witness then tries to identify the perpetrator in question from his or her picture. If the witness identifies one photo, the picture is distributed to local law enforcement officials who are searching for the criminal, and the board is kept as evidence.
When law enforcement officers create a mug book, they must follow certain procedures to make sure no photograph stands out. If a picture is different from the ones around it, that difference could prejudice the witness. Color pictures are kept separate from black and white, and pictures are grouped by size.
Mug books are also divided out by characteristics such as gender, race, age, and even hair color. If the witness reported a man committed a crime, then law enforcement officers will only show them mug shots of men, not women. The division will be as specific as the information from the witness allows.
Occasionally, police form mug books divided by specific crimes. Since many criminals are repeat offenders, a search can often be shortened by first looking at people who were arrested for similar crimes in the past. This is particularly common among sex offenders.
Computerized imaging systems are slowly replacing traditional mug books in many places around the world. These systems store all mug shots and sketches of criminals and organize them into different categories. Officials can quickly narrow down the pictures involved by selecting certain criteria. This allows law enforcement officials to quickly search the database and create a picture spread.
In the United States, the fourth amendment protects suspects against unreasonable searches and seizures. Law enforcement must be able to demonstrate probable cause in order to receive a search warrant to gather evidence. Since a person’s appearance is public knowledge, it is not protected by the fourth amendment. Therefore, a mug book is considered legal evidence.