While the interviews of the police officials attracted far more attention — and led to discipline on Thursday against four senior department officials — the examination of the roles of the businessmen, according to several people briefed on the matter, and the mayor’s fund-raising have been the central elements of the inquiry.

Image Hamlet Peralta in 2008. Credit... Mark Von Holden/WireImage, via Getty Images

The sprawling investigation also led to the arrest this week of a Manhattan restaurateur with ties to Mr. Rechnitz and Mr. Reichbach. He was charged in an unrelated Ponzi scheme whose investors included the two men, according to a criminal complaint filed in the case and a person briefed on the inquiry.

The restaurateur, Hamlet Peralta, who owned the now-closed Hudson River Café in Harlem, misappropriated more than $12 million from investors for use in what he said was a wholesale liquor business, according to the complaint, which was unsealed on Friday in Federal District Court in Manhattan. The business was, in fact, fictitious, prosecutors said.

Mr. Peralta, 36, used more than $11 million of the money to repay other investors and to cover personal expenses like high-end clothing purchases, restaurant bills, gas and spa treatments, according to the complaint, which was filed by the office of Preet Bharara, the United States attorney for the Southern District of New York, which is conducting the broader inquiry along with the F.B.I.

Mr. Peralta, who faces one count of wire fraud, was arrested on Thursday by F.B.I. agents in Macon, Ga.; on Friday, a magistrate judge ordered him detained and sent to New York for further proceedings. A lawyer who represented him in court on Friday declined to comment.

According to the complaint, Mr. Peralta relied on a recruiter to help him find investors, and he befriended at least one other person who became an investor at his restaurant. That person was one of Mr. Peralta’s largest investors and gave him more than $3.5 million, the complaint says, adding that Mr. Peralta still owes that investor more than $1.5 million.

The complaint, signed by Joseph Downs, an F.B.I. special agent, said that the authorities identified about 12 investors in the scheme, none of whom were named in the document. But the person briefed on the inquiry, who spoke on the condition of anonymity because that person was not allowed to discuss the matter, said the investors included the two businessmen, Mr. Rechnitz and Mr. Reichberg.