Jona S. Rechnitz, the scion of a wealthy Los Angeles family, came to New York City about a decade ago to make his mark. A brash young man eager to fund philanthropic causes, he cultivated connections with the Police Department — posing with top officials, and once arranging for police bagpipes at a party — and became a fixture at fund-raising events for Mayor Bill de Blasio.

Jeremiah Reichberg came from the more cloistered world of Borough Park, Brooklyn, an Orthodox Jewish enclave where he was a familiar presence, even if his private life and business dealings were not well known. He ran a consulting firm, and hosted Mr. de Blasio to great fanfare at his home in 2014 for a fund-raising event.

Mr. Rechnitz and Mr. Reichberg became close, appearing together at public and private events, and serving on Mr. de Blasio’s inauguration committee — an honor bestowed on the famous, like the writer Junot Díaz and the actor Steve Buscemi, and on lavish givers. In recent weeks, they have become the fulcrum of a sprawling federal corruption investigation into the mayor’s fund-raising activities and the actions of police commanders.

The federal inquiry, which began in 2013, has laid bare the city’s nexus of political influence and campaign donations, dormant for a decade during the administration of the billionaire Michael R. Bloomberg, as well as the world of those men, like Mr. Rechnitz and Mr. Reichberg, who sidle up to police officials as a kind of informal currency. The two men — neither of whom has been charged with a crime — appeared to take great pride in the closeness with which they spoke to senior commanders, including Philip Banks III, once the top chief, who has come under scrutiny as part of the inquiry.