CHICAGO – The family problems facing alleged Chicago loan shark Frank Calabrese Sr. make Tony Soprano’s seem mild.

Calabrese and four other men are on trial in a Chicago mob case prosecutors have dubbed “Family Secrets.” The government’s key witnesses: Calabrese’s son, Frank Jr., and his brother, Nicholas.

Prosecutors built parts of their case around secrets they say Frank Jr. and Nicholas helped spill. One of the other defendants even claims he’s the victim of a dysfunctional family’s feud.

Seventy-year-old Frank Sr. and the four other men – James Marcello, 65; Joseph (Joey the Clown) Lombardo, 78; Paul Schiro, 69, and Anthony Doyle, 62 – are charged with racketeering acts including 18 murders dating back to the 1970s and 1980s.

The enterprise, according to the indictment, is the Chicago Outfit, the city’s organized crime family founded in the Prohibition Era by Al Capone.

All five defendants have sworn to fight the charges.

The proceedings got off to a surprising start last week during jury selection when word arrived concerning still another Calabrese relative.

Frank Sr.’s other son – Kurt – arrived at his home in the plush Chicago suburb of Kenilworth to find a plastic bag containing a digital clock, some wires and items resembling sticks of dynamite on his doorstep.

The bomb was a fake, and authorities have not said if they have any suspects.

The story of how the Calabreses started turning on one another traces back to 1995, when Frank Sr. and his two sons, Frank Jr. and Kurt, were charged with Uncle Nick in a federal loan-sharking indictment. All four pleaded guilty to roles in the family business.

“All I want to do is get my family back together,” Frank Sr. told U.S. District Judge James Holderman, who sentenced him to almost 10 years in prison.

But it was while he was in prison that his family woes got worse.

Frank Jr. was in the same federal prison, at Milan, Mich., and as the father and son walked around the exercise yard Frank Sr. allegedly spoke about some of the mob’s darkest secrets – including long-unsolved murders.

Unknown to Frank Sr., his son was taping their conversations and jurors at the Family Secrets trial are expected to hear what was said.

Meanwhile, Nicholas was facing a murder charge and federal prosecutors were pressuring him to save himself and break the mob’s code of silence.

Prosecutors allege that for a time Marcello was paying $4,000 a month to the jailed Nicholas’s wife to buy his silence – especially about Marcello’s alleged role in the murder in June 1986 of Tony “The Ant” Spilotro, once known as the Chicago Outfit’s man in Las Vegas.

Nicholas eventually agreed to plead guilty and take the witness stand against his brother. As a so-called made guy who has taken the mob oath and goes back a long way, he appears to be in a position to tell secrets.

In his opening statement on behalf of Calabrese, attorney Joseph Lopez sought to discredit both Frank Jr. and Nicholas, hanging the family laundry out for the world to see.

Lopez predicted that Frank Jr. would flay his father on the stand.

“He’s gonna say my father is a rotten S.O.B., my father never loved me,” Lopez told jurors. “None of that is true.”

He said jurors will be shown letters between father and son demonstrating “their love for each other.”

But even Lopez admitted it wasn’t all sweetness and light.

“You’re gonna hear that Frank did slap his son around on numerous occasions,” he said. But he said that was only because he caught young Frank Jr. robbing the neighbors of their jewelry and smoking crack.

“The man sitting there in the powder blue suit could be a cheese salesman from Wisconsin,” Lopez told jurors of his client, whom he portrayed as a deeply religious, good-hearted family man.

Federal prosecutors, though, say he’s no cheese salesman.

Assistant U.S. Attorney John J. Scully told jurors in the government’s opening statement about a specific technique Calabrese is alleged to have used when he murdered some victims. He would strangle them with a rope then cut their throats to make sure that they were dead, the prosecutor said.

The Calabrese family’s roots are on the South Side, in the shadow of U.S. Cellular Field, home of the Chicago White Sox. Investigators say the neighborhood was a hotbed of the mob.

“Everybody knew everybody,” says Lee Flosi of Quest Consultants International, a private company made up entirely of former FBI agents that conducts investigations for corporate and political clients.

“You especially knew who the wiseguys were – the cars they drove, the clothes they wore – they needed them to get the respect they had to have,” says Flosi. He says Frank Sr. was long known to the FBI as the top loan shark for the mob’s 26th Street Crew, also known as the Chinatown Crew.

FBI agents once ripped up the concrete in one of the White Sox stadium’s parking lots, hoping to find the bones of murdered mob loan shark Michael “Hambone” Albergo.

Prosecutors say Frank Sr. and others murdered Albergo in August 1970. But agents were unable to find Albergo’s remains under the parking lot.

In all, the indictment accuses Frank Sr. of 10 murders.

Taking note of the Calabrese family’s woes, Marcello attorney Marc Martin said his client might not even be in court if not for their problems.

“My client,” he said, “got caught in the crosshairs of a dysfunctional family.”