Becoming a detective starts by first becoming a police officer and serving in a conventional patrol capacity. It is during the training, probationary, and patrol periods that police officers gain an understanding and appreciation for the criminal process, the criminal justice system, and the role of the law enforcement community.Becoming a detective starts by first becoming a police officer and serving in a conventional patrol capacity. It is during the training, probationary, and patrol periods that police officers gain an understanding and appreciation for the criminal process, the criminal justice system, and the role of the law enforcement community.