(CNN) Donald Trump's glittering empire of New York skyscrapers and Atlantic City casinos have long had a darker side, allegations that the mob helped build them.
Trump's alleged ties to New York and Philadelphia crime families go back decades and have been recounted in a book, newspapers and government records.
"The mob connections of Donald are extraordinarily extensive," New York investigative journalist Wayne Barrett told CNN in an interview.
Barrett, the author of the 1992 unauthorized biography "Trump: The Deals and the Downfall," wrote that Trump's life "intertwines with the underworld."
The allegations are getting new scrutiny as Trump runs for president, largely on his record as a successful, and extraordinarily wealthy, businessman. As Trump cements his leads atop the polls, questions about how he made his billions, and who helped him make them, are starting to take center stage.
A Trump spokesperson did not respond to multiple requests for comment on this story.
To be sure, organized crime had ties to the New York and New Jersey construction industry in the 1980's and early 1990's, making contact between developers and mafia-controlled companies almost unavoidable at times.
"There was a certain amount of mob association during which the father and he were building, which was very difficult to avoid in the New York construction world," Barrett said, adding, "He went out of his way not to avoid them, but to increase them."
In a recent Federalist article, David Marcus writes that Trump bought the property that his Atlantic City casino Trump Plaza would one day occupy -- for twice market price -- from Salvatore Testa, a Philly mobster and son of one-time Philly mob boss Philip "Chicken Man" Testa. (Springsteen fans might recognize the elder Testa from the opening lines of the song, Atlantic City.)
In his book, Barrett writes that Testa and a partner, who together headed a Philly mafia hit-squad called the Young Executioners, bought the property for "a scant $195,000" in 1977. In 1982, Trump paid $1.1 million for it.
"The $220 per square foot that Trump paid for the Testa property was the second most expensive purchase he made on the block, even though it was one of the first parcels he bought," Barrett wrote.
The casino was built with the help of two construction companies controlled by Philly mobsters Nicademo "Little Nicky" Scarfo and his nephew Phillip "Crazy Phil" Leonetti, according to, as Marcus notes, a New Jersey state commission's 1986 report on organized crime.
Trump also had a decade-long relationship with Scarfo's investment banker, according to Barrett's book.
In Manhattan, Trump used the mob-controlled concrete company S&A to build Trump Plaza condos. Anthony "Fat Tony" Salerno, head of the Genovese crime family, and Paul Castellano, the don of New York's Gambino family, controlled S&A, according to federal court records Barrett cited in his book.
Barrett noted that he built the Trump Tower out of concrete, instead of steel, at a time when the mafia controlled much the concrete industry.
"While dealing with the concrete cartel was inevitable for any developer in the period when Trump Tower was built, Donald took the relationship several steps further than he had to," Barrett wrote.
In a Philadelphia Inquirer article from the time the book was published, reporter David Cay Johnston summed up Barrrett's unauthorized biography, writing that it "asserts that throughout his adult life, Donald Trump has done business with major organized-crime figures and performed favors for their associates."
Trump was a target of a 1979 bribery investigation and was questioned in a 1981 racketeering probe, but neither federal investigation led to criminal charges, Johnston wrote.
More recently, Johnston, a Pulitzer-prize winning journalist, wrote an article called "21 Questions for Donald Trump" where he asked, "Why did you use concrete instead of steel girders" to build the 58-story Trump Tower?