NEW YORK — It is perhaps the most intriguing unsolved mystery from the gaudy gangland career of John Gotti: Whatever happened to the neighbor who accidentally ran over and killed the mobster’s 12-year-old son — and then vanished?

According to papers filed this week in Brooklyn federal court, John Favara was shot to death on orders of the outraged Gambino crime family chief and his body was dissolved in a barrel of acid. Authorities said a cooperating witness identified Charles Carneglia, a 62-year-old former mobster, as the perpetrator in the 1980 incident.

The court documents said Carneglia told another informant that acid was “the best method to use to avoid detection.”

Those details, in a 44-page evidence motion by federal prosecutors for a racketeering trial, offered a new twist on the fate of Favara, a 51-year-old furniture warehouse worker who lived near the Gottis in the Howard Beach section of Queens.

Favara was arriving home from work on March 18, 1980, when Gotti’s son Frank, riding a minibike, darted in front of his car. The driver told police he was momentarily blinded by the sun and did not see the boy.

The crash was ruled an accident by police, but Favara was subjected to death threats and harassment for months. His car was stolen and later smeared with the word “murderer,” and he was threatened by Gotti’s bat-wielding wife when he tried to apologize.

However, he ignored suggestions that he should move away.

Five months later, on July 28, 1980, Favara disappeared after leaving work on Long Island and no trace of him was ever found. Witnesses saw him being beaten and heard tires squealing. The Gottis gave police hotel receipts showing they were in Florida on that date, and no arrests were ever made.

Carneglia, according to the court documents, was part of a seven-member hit squad that committed murders on order and disposed of the victims. He faces trial for racketeering and five murders.

The prosecutors’ motion, signed by Assistant U.S. Attorney Roger Burlingame, includes Favara’s case among several “uncharged crimes.” Carneglia has pleaded not guilty.

The new revelation raises yet another question for experts who have been studying gangland activities.

Jerry Capeci, an author and expert on the Mafia who has written extensively on Gotti, asked: “What kind of acid could be used in a metal drum without leaking?”