Hartford — A reputed mobster from Connecticut suspected of having knowledge about the largest art heist in U.S. history lost a bid Wednesday to get a weapons case dismissed.

Robert Gentile, 79, claimed federal authorities entrapped him into illegally selling a gun to pressure him into cooperating in the investigation of the still-unsolved 1990 theft at Boston's Isabella Stewart Gardner Museum. Thirteen pieces of art worth an estimated $500 million were stolen, including paintings by Rembrandt, Edouard Manet, Edgar Degas and Johannes Vermeer.

The artwork remains missing and no one has been charged in the theft.

Gentile has consistently denied knowing anything about the missing art. Federal prosecutors, however, said they have evidence that shows otherwise, and disclosed for the first time Wednesday allegations that Gentile discussed the missing paintings with fellow inmates in prison.

U.S. District Judge Robert Chatigny in Hartford on Wednesday rejected Gentile's request to dismiss the weapons case. Gentile's lawyer, A. Ryan McGuigan, argued that the government entrapment of Gentile was so "outrageous" that it warranted throwing out the charges.

Assistant U.S. Attorney John Durham denied McGuigan's claims and told the judge that it was not unusual for authorities to charge someone with a crime in an effort to get cooperation with another case.

Chatigny said similar efforts to get cases dismissed based on claims of outrageous government conduct have rarely been sucessful.

"This is not a case in which I need to be concerned about the targeting of an innocent person," Chatigny said. "I think that there is a legitimate law enforcement interest in attempting to recover the paintings."

Gentile did not speak during or after the hearing. He was in a wheelchair and wore a beige prison jumpsuit.

Durham has previously said Gentile told an undercover FBI agent that he had access to two of the stolen paintings and could negotiate the sale of each for $500,000. Durham said Gentile made the offer after he was released from prison in April 2014, when he finished a sentence in a different weapons and prescription drug case.

On Wednesday, Durham revealed that authorities have evidence that Gentile, who remains detained without bail, talked about the paintings with at least three fellow prisoners at the private Wyatt Detention Facility in Rhode Island, including giving them information on who to call about the art and what code name to use.

McGuigan has alleged that because the FBI believes Gentile has not been forthcoming with everything he knows about the heist, the agency has set him up for arrests twice in the last three years.

Gentile, who authorities said is a made member of the Philadelphia mob with a criminal record dating to the 1950s, is charged with selling a loaded .38-caliber revolver for $1,000 to a cooperating government witness at his home in Manchester last March. He has pleaded not guilty.

In May 2013, Gentile was sentenced to more than two years in prison for illegally selling prescription drugs and possessing guns, silencers and ammunition. In that case, Durham said federal agents found in Gentile's home a handwritten list of the stolen paintings and their estimated worth, along with a newspaper article about the museum heist a day after it happened.

Authorities also searched Gentile's property with ground-penetrating radar in what McGuigan has called a veiled attempt to find the stolen artwork, but didn't find the paintings.

The Boston museum continues to offer a $5 million reward for the return of the artwork.