NEW YORK CITY (TIP): A federal investigation into Mayor Bill de Blasio‘s campaign fund-raising has recently secured the assistance of Harendra Singh, owner of Water’s Edge restaurant in Queens, who has been indicted on unrelated federal fraud and bribery charges, according to a report by The New York Times.

The Federal Bureau of Investigation and the office of the United States attorney in Manhattan, Preet Bharara, are conducting the inquiry.Investigators have zeroed in on whether donations were exchanged for beneficial city action in several cases. But so far they could not gather sufficient evidence to bring criminal charges against de Blasio or his aides to prove that they took official action for donors in exchange for aids to his nonprofit or to his campaign.

Harendra Singh and another donor Jonah Rechnitz were cooperating with the inquiry in an effort to obtain leniency for their own crimes, says the report. Singh already faces federal charges that he bribed a Town of Oyster Bay employee to get loan guarantees for two food concessions, and fraudulently collected $1 million in Sandy disaster aid for the Queens restaurant, Water’s Edge, which closed last year.

In 2011 and 2013 Singh hosted de Blasio fundraisers inWater’s Edge. The Mayor got over $50,000 in political donations from Singh, his family and associates, and named Singh to his inaugural committee and other advisory posts.

In September 2015 Singh was arrested on numerous charges and after eight months’ detention he was released form jail in August