B O S T O N – As Sens. John Kerry and John Edwards arrived in Boston today for the Democratic National Convention, so did the California man who is their single biggest contributor. He is Stephen Bing, a wealthy film producer who, with little fanfare, has managed to steer a total of more than $16 million of his money to Democratic candidates and the supposedly independent groups that support them.

“To most of the people who track money and politics, they’re like, who the hell is Steve Bing?” said Chuck Lewis, founder of the Center for Public Integrity, a nonprofit, nonpartisan watchdog organization.

Bing is perhaps best known for sparking a tabloid frenzy when he publicly expressed doubt that he was the father of actress Elizabeth Hurley’s baby. (A paternity test proved he was indeed the father.) He repeatedly has refused to say why he is funneling millions of dollars to the Democrats.

Lewis thinks it is cause for concern.

“We can identify who the big donors are, but how much do we really know about any of them?” he said.

In fact, Democratic Party officials said they knew nothing about the man who law enforcement officials tell ABC News is Bing’s friend and business partner – Dominic Montemarano, a New York Mafia figure currently in federal prison on racketeering charges.

Montemarano has a long criminal record and is known to organized crime investigators by his street name, Donnie Shacks.

“Donnie Shacks’ main activity was murder. No question about it. That was his main function for the Colombo family and for organized crime in general. He was one of the top hit men in the New York area,” said Joe Coffey, a former NYPD investigator.

According to The Los Angeles Times, Bing paid Montemarano’s legal fees after his most recent scrape with the law. Montemerano’s lawyer said his client was an employee of Bing’s.

After a recent private lunch with Democratic vice-presidential candidate Edwards, Bing also declined to answer questions about his relationship with Montemarano. “The American people have a right to know who’s funding their presidential candidates and their parties,” Lewis said. “The Bing situation shows us how little we really know.”

Throwback to Nixon Days?

Campaign reform advocates say the role of secretive big money is all a throwback to the days of Richard Nixon and the scandal that grew out of the 1972 Republican Convention.

The telephone company that helped pay the costs of that convention, ITT, later got favorable consideration on an antitrust issue, when it became the world’s largest conglomerate.

“It raised a huge public outcry and led to basic reforms which said the public funds will be used to pay for these conventions, but that’s the only money you can use,” said Fred Wertheimer, president and founder of Democracy21.com, a nonpartisan watchdog organization.

He added: “Today, we’ll have over $100 million from corporations and other special interests helping to fund these two national conventions.”

For the Democrats, some $40 million in corporate money, in addition to $15 million in public funds, is underwriting their national convention – a no-expenses-spared operation.

There are even two private trains underneath the convention floor, courtesy of the railroad industry, with luxury club cars serving as cocktail and cigar lounges for top Democratic officials.

“This is money to curry favor, to gain influence,” said Wertheimer. “The very thing that the Watergate laws were designed to stop.”