Memo to Mobsters: Don't "Adopt" Anyone - He May Turn Out to be a Rat

Memo to mobsters: Don't "adopt" anyone - he may turn out to be a rat.

John A. (Junior) Gotti learned that the hard way with "adopted" son Lewis Kasman, who taped Gotti family meetings for the feds.

Reputed killer Charles Carneglia is about to get a taste of the same medicine with "adopted" kid brother Kevin McMahon.

Both mob turncoats are to testify in Carneglia's ongoing murder trial in Brooklyn Federal Court.

Kasman, a former Long Island garment exec who wormed his way into Gotti's inner circle and called himself the adopted son of the late Gambino crime boss, wasn't close to Carneglia.

McMahon was as close as you can get without being a relative. "When Kevin walks into that courtroom I would expect Charles will want to jump over the table and strangle him," a law enforcement official said.

McMahon was not only a member of Carneglia's crime crew, he was like a member of the Carneglia family.

In 1980, McMahon was a 12-year-old Irish kid from Howard Beach "at the beginning of his long and extraordinarily close relationship" with Charles Carneglia and his brother John, court papers show. McMahon is 20 years younger than Charles, 62, and John, 64.

On a fateful day in March, McMahon lent his minibike to mob scion Frank Gotti who was accidentally hit and killed by neighbor John Favara as he drove home from work. Favara was slain on Gotti's orders and, prosecutors say, Charles Carneglia dissolved his body in a barrel of acid.

Before the incident, McMahon had been "informally adopted" by John and Charles Carneglia. Charles Carneglia promised to protect the lad from retaliation for his role in Frankie's death.

McMahon was treated as a member of the Carneglia family, living with them for long stretches, attending family dinners and going on Carneglia family vacations, Assistant U.S. Attorney Roger Burlingame said.

Former capo Michael DiLeonardo has testified that McMahon was a "goofy kid" who taunted FBI agents, running up to them and grabbing his crotch.

McMahon had jobs with Local 638 steamfitters union and Local 52 motion pictures mechanics union, but those paid only $40,000 a year, chump change for a wanna-be Gambino associate with an ailing wife and two kids.

Prosecutors say he and Carneglia took part in extortions, art fraud and robberies, including the stickup of an armored car at Kennedy Airport in 1990 in which guard Jose Rivera Delgado was shot to death. McMahon dropped a baseball cap at the scene. DNA tests linked him to a strand of hair in the hat.

Shortly after he was arrested in 2005 on an indictment charging him with racketeering for the Gambinos in Tampa, McMahon sent a "thank you" letter to Brooklyn Magistrate Robert Levy for releasing him on bail.

"As I was leaving the courtroom you said to me, 'Don't let me down.' I assure you I have not," he wrote. "As soon as I'm acquitted I'll write you again."

McMahon turned on his adoptive mob family after he was convicted and faced 20 years behind bars. He is cooperating in hopes of winning a lesser prison term.

Thanks to John Marzulli