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"There have been multiple media reports about Donald's business dealings with the mob, with the mafia," Cruz said Sunday on ABC's "This Week." "Maybe his tax returns show that those business dealings are a lot more extensive than reported. We don't know."
Cruz pointed to S&A Concrete, which built Trump Tower, and other media reports linking the billionaire businessman to the mafia.
"You guys have reported that he's done deals with S&A Concrete, which was owned by two of the big crime families in New York and that he's had involvement in Atlantic City," Cruz said. "Maybe that's what his tax returns show. We don't know."
The Trump campaign has not yet responded to a request for comment.
An ABC News investigation found Trump claimed to not know Felix Sater, a twice-convicted Russian émigré who served prison time and had documented mafia connections, while testifying in video deposition for a civil lawsuit two years ago. Sater had played a role in a number of high-profile Trump-branded projects across the country.
Cruz added conservatives should unite behind him if they don't want Hillary Clinton in the White House.
"In the general election, Hillary Clinton is going to shine a light on all of this and Republican primary voters deserve to know,” Cruz said.