Mayor Gaynor found a new Deputy Commissioner named William J. Flynn, formerly of the federal Secret Service. Gaynor brought him in to apply Secret Service tactics to fighting crime in New York.

In a little more than three months, “Secret Service Flynn”… head of the city’s detective forces, has revolutionized the methods of detecting crime in New York. He is perfecting a secret service that is really secret. He is doing it in spite of the legal limitations that force all of his men into one physical mold. It is being done without precedents, except the Federal Secret Service. The results have been arrests of gamblers by hundreds and other offenders by scores, even while the reorganization was in progress.

“It’s a tough job, but I’m going to give it a wrestle,” remarked Flynn when he took the office last October. “I’ll stake my reputation and a lot of hard work on making good. I have in mind an entirely new plan of work — new to the Police Department. Haven’t got the details worked out yet.”

A year later, he returned to the US Secret Service as Chief, and eventually became head of the FBI.

SECRET SERVICE METHODS IN NEW YORK’S POLICE SYSTEM: What Deputy Commissioner Flynn Has Done and Is Doing in Reorganizing the Detective Force Along Lines Followed by the U. S. Government (PDF)

From February 26, 1911