The witness who helped the federal investigators crack an alleged bribery plot by two New York City politicians reportedly is a real estate investor who owes nearly $130 million to Citigroup.

DNAinfo.com New York reported on Wednesday that Moses Stern set up the backroom deals that allegedly included tens of thousands of dollars in payoffs and a plot to get state Sen. Malcolm Smith, a Democrat, on the Republican ticket for this year’s mayoral election.

The news site reports that Stern’s negotiations led to Tuesday’s arrests of Smith and Queens councilman Dan Halloran.

In spring 2007, during the height of the real estate bubble, Stern got Citigroup to give his firm, First Republic Group Realty, a staggering $126 million in mortgage loans to buy 11 strip malls in the Northeast despite a shoddy investment track record, DNAinfo.com reported. One source described Stern to the news site as "a good businessman" but untrustworthy.

"You know the saying, when you shake his hand, when you pull your hand back, check to see if all your fingers are there," the source said.

Click here for more from DNAinfo.com New York