Public corruption cases making headlines across New York are old news to a little-known group of lawmen who work in state and federal prosecutors' office.

Career investigators have been behind some of the most notorious investigations in New York City history — though they're largely unknown outside law enforcement circles.

State district attorney investigators called DIs can trace their roots back to the 1930s-era racket busters under the famous DA Thomas E. Dewey.

And former Manhattan District Attorney Robert Morgenthau said he hired criminal investigators during his stint as a U.S. attorney in the 1960s to take on such cases.

City DIs have played key roles in probes into bank money laundering, Albany lawmakers' corruption, decades-old wrongful conviction cases and Mafia prosecutions.