What is Mr. de Blasio’s connection to the investigations?

At the heart of each of the five inquiries is money — in most cases, fund-raising linked to the mayor, his election campaign or a nonprofit group connected with him.

Mr. de Blasio, a Democrat elected in 2013, has made no secret of his attempts to raise significant sums to bolster his agenda through that group, the Campaign for One New York, and through an effort in 2014 to wrest control of the State Senate from the Republicans by supporting several Democratic candidates. Donors to the mayor’s political endeavors include major unions and real estate developers, and many of them have business before the city.

It is not clear how direct a role, if any, the mayor played in some of these matters. The inquiries that seem closest to him focus on two issues: the effort to help Senate Democrats, and the relationship he had with Nyclass, an animal-rights group that spent heavily in the 2013 mayoral race against Mr. de Blasio’s chief rival, Christine C. Quinn.

Two of the main backers of that effort, Steven Nislick and Wendy Neu, have contributed to Mr. de Blasio’s nonprofit. Ms. Neu has given at least $75,000 and Mr. Nislick $50,000.