article: A 78-year-old Connecticut man with a long criminal history was arrested on Friday, but the man's lawyer claimed the arrest was a ruse intended to pressure him to talk about the biggest art heist in U.S. history. Robert Gentile appeared in federal court in Hartford, . Connecticut, on Friday and was charged with selling a firearm to . an undercover agent. His attorney, Ryan McGuigan, contended Federal Bureau of . Investigation agents really want to see what Gentile knows about the . theft of $500million in artwork from Boston's Isabel Stewart . Gardner Museum 25 years ago. Scroll down for video . Robert Gentile's attorney Ryan McGuigan (pictured), said that though his client was arrested on a gun charge, he believes the arrest was a ruse to pressure Gentile to speak about the $500million art heist from 1990 . A security guard at Boston's Isabella Stewart Gardner museum stands outside the room from which most of the paintings were pilfered the day after the massive heist . This FBI sketch shows a likeness of the two suspects, who were reportedly wearing police uniforms when they performed the theft. They have have never been caught . 'The FBI has been questioning him for years because they . think he knows the whereabouts of the Gardner paintings,' McGuigan said. He added: 'But he's being set up, just like others who are . threatened with long periods of incarceration by the FBI in the . Gardner case. 'The gun charge is just an excuse to question and . threaten him further.' Police previously identified three suspects in the theft: Carmello Merlino, Robert Guarente, and Robert Gentile. Merlino and Guarente have died. Gentile has denied any knowledge of the heist and the missing work. The thieves stole two Rembrandts - The Storm on the Sea of Galilee (left), believed to be the only seascape the master painted, and A Lady and Gentleman in Black. Jan Vermeer's The Concert (right) was also stolen and is one of approximately 35 known works by the great Dutch painter . Chez Tortoni, painted by Manet, shows a man wearing a top hat at a jaunty angle; it was one of the last paintings to be stolen from the museum . Govaert Flinck's 'Landscape with an Obelisk,' painted in 1638, was originally attributed to Rembrandt, but was later found to be the work of his assistant, Flinck . The FBI and U.S. Attorney's Office in Connecticut declined . to comment on McGuigan's claim. The Gardner heist took place on the rainy night of March 18, . 1990, when two men posing as police officers arrived at the . museum's front door. The guards on duty let them in and the pair . allegedly overpowered them, one of whom spoke earlier this year about his guilt of letting the men in. The next morning the guards were found duct-taped to chairs . in the basement and 13 artworks including Rembrandt van Rijn's 'Storm on . the Sea of Galilee' and Johannes Vermeer's 'The Concert' were missing. A Degas sketch from 1884 (left) and a self-portrait of Rembrandt (right) were also among the items stolen from the museum . The empty frames from Rembrandt's 'Storm on the Sea of Galilee' and Vermeer's 'The Concert' remain on display in the museum as a constant physical reminder of the heist and the missing masterpieces . Left, a visitor looks at the empty frame from a Rembrandt work, and right, the museum pictured in 1990 following the heist, the empty frame of Rembrandt's oil painting 'A Lady and Gentleman in Black' lies on the floor and a space on the wall remains bare where his 'The Storm on the Sea of Galilee' once hung . In total the haul including three Rembrandt works, five sketches by Edgar Degas, an Édouard Manet painting and a painting by Vermeer - one of only 36 in the world. A bronze eagle statue, a Chinese beaker from 1100 BC and a painting by Govaert Flinck were also taken. Due to a quirk in the museum founder's will, the empty frames that once held those paintings remain on the walls, an ever-present reminder of one of Boston longest-unsolved crimes. Aside from two sketches of mustachioed men in police hats - one with glasses and one without - little detail has ever been given as to who the thieves may have been. The FBI identified three persons of interest in the Gardner case, all with ties to organized crime: Carmello Merlino, Robert Guarente, and Robert Gentile. In 2012 Robert Gentile's Connecticut home and shed (pictured) was searched by the FBI in connection with the case . gents used radar, as well as two beagles and a ferret, to dig up parts of Gentile's front lawn in 2012; the FBI warrant allowed the use of ground-penetrating radar . FBI investigators have long said they believed organized . crime groups were behind the heist. Gentile in 2012 submitted to a lie detector test that showed . a high likelihood that he had lied when he investigators asked . if he had any knowledge of the heist, according to court . testimony. A 2012 FBI search of Gentile's home turned up a list of the . stolen art pieces and their estimated value, as well as police . uniforms. Gentile has a criminal record dating back to the 1950s. Most . recently he spent two years in prison after being convicted of . illegally selling prescription drugs to an informant. The gun charge he currently faces could carry a ten-year prison charge if he is convicted due to his status as a felon. The FBI search of Gentile's home turned up a list of the stolen art pieces and their estimated value, as well as policeuniforms . The FBI, pictured here in 2013, has actively offered a $5million reward to anyone who had information that led to the painting's safe return to the museum .
highlights: Robert Gentile was  charged with selling a firearm to an undercover agent .
  But his attorney claims the arrest was a ruse  to get Gentile to talk about the 1990 Boston art heist at the Isabel Stewart Gardner Museum .
  Gentile's house was searched in 2012 and police found a list of the stolen art pieces and their estimated value, as well as police uniforms .
  The half-a-billion heist remains unsolved and FBI has never  come close to finding thieves .
  Gardner museum continues to display empty frames, and is offering $5million reward for the return of the works .
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