New York City's first plainclothes police officers, hired in 1836 to detect crime, were officially called roundsmen and quickly dubbed “shadows” by citizens impressed by their talents.

Two decades later, 20 uniformed police officers were officially designated detectives and assigned to a separate unit within the larger metropolitan police force. They were divided into squads, each squad charged with the investigation of specific crimes.

Detectives used to regularly scour large crowds for known pickpockets, whom they were instructed to arrest on sight. Members of the public were encouraged to tour the notorious “Rogues Gallery,” a photographic smorgasbord of the era's criminals and forerunner to today's mug shots.

In 1882, the state Legislature formally created the Detective Bureau and appointed Thomas Byrnes, the first Chief of Detectives. An Irish immigrant who rose through the ranks and masterfully lobbied lawmakers to create the Bureau, Byrnes was celebrated as a savvy police commander. He was extremely knowledgeable about the denizens of the city's criminal underclass. As a captain, he was credited with solving the Bank of Manhattan burglary, arresting most of the perpetrators and recovering a sizable portion of the loot -- $3 million in cash and securities. “There is no such thing as honor among thieves,” Byrnes is quoted as saying: “I never met a thief in my life, provided he could benefit by poaching on confederates, from whom I could not find out anything I was desirous to know.”

Although a corruption scandal which engulfed the entire department tainted his accomplishments, Byrnes was heralded as a capable administrator who, in the words of journalist Jacob Riis, “made the detective service great.”

Heroic Undercover