A reputed Connecticut mobster linked to artwork stolen from a Boston museum in 1990 was arrested Friday on a gun charge, and his defense attorney said it was likely related to federal authorities' efforts to press him for information they claim he has on the Isabella Stewart Gardner Museum heist.

Robert Gentile, 78, was arrested as he met with probation officials and charged with selling a weapon to an undercover agent, according to his attorney, A. Ryan McGuigan.

"It would be a hell of a coincidence" if the arrest is not related to the investigation into the missing artwork, McGuigan said.

Gentile was sentenced to prison in 2013 in a weapons and prescription drug case that revealed federal prosecutors' belief that he knows something about the heist of artwork worth an estimated $500 million.

Gentile has denied having any knowledge of the robbery.

FBI officials have identified Gentile as the last surviving person of interest in the Gardner heist, in which two men posing as police officers stole 13 pieces of artwork including paintings by Rembrandt van Rijn, Edouard Manet, Edgar Degas and Johannes Vermeer. No one has been charged in the art theft, and the paintings have never been found.

When federal agents searched Gentile's house in Manchester in 2012, they found a handwritten list of the stolen paintings and their estimated worth, according to prosecutors, who also said a polygraph test showed there was a 99 percent chance that Gentile was lying when he denied knowing where the paintings were.

McGuigan has questioned the validity of the polygraph test and insisted that Gentile wasn't a made member of the mafia.

Gentile is scheduled to appear Friday afternoon in federal court in Hartford, according to the U.S. attorney's office.