Investigation represents an individual's proficiency at deductive reasoning. In most cases, this skill is applied to the arena of criminal investigation. Classes of people known to possess this talent include detectives, secret agents, police inspectors, private investigators, and pulp era gumshoe detectives. Modern techniques implemented in criminal investigation have their roots in 19th century Victorian England. Famed British sleuth Sherlock Holmes often worked on behalf of Scotland Yard preferring the practice of gathering information through astute observation rather than through clinical research. Holmes’ methods were imitated by others, and paved the way for future generations of detectives.
By the 1930s, the United States saw an upsurge of would-be investigators establishing themselves in private practice. Hard-hitting private dicks such as Slam Bradley, Bruce Nelson, and Buck Marshall appeared in nearly every major city. Other adventurers such as Speed Saunders and Bart Regan also honed their investigative talents to further their respective careers.
The art of investigation evolved greatly over the years, and new techniques and processes were being developed all of the time. Investigation is no longer confined to the art of simple sleuthing. It now incorporates scientific processes such as cryptography, stenography, computer networking, analysis etc. It also involves more intelligence-related applications including interrogation, disinformation, surveillance, concealment, infiltration and communications.
By the standards of the modern era, the costumed vigilante Batman is considered by and large to be the world's greatest detective. He is a master of nearly every technique involved in criminal investigation and has solved countless mysteries and crimes throughout his long career.
The computer age practically changed the entire dynamic of investigation techniques, and many investigators, both in the government and the private sector, perform their best work from behind the scenes. While Batman may be considered the best criminal detective, few would debate that his close ally Barbara Gordon is the foremost authority on computerized investigation and network analysis.