HARTFORD, Conn. (Reuters) – An 81-year-old alleged mobster who police believe may be able to solve the largest art heist in U.S. history was sentenced on Tuesday to 4-1/2 years in prison after pleading guilty to illegally selling guns to a convicted murderer.

Robert Gentile admitted last year to illegally selling a loaded firearm to a convicted killer. His lawyer said he was caught in a Federal Bureau of Investigation sting aimed at pressuring him into providing details on paintings stolen from Boston’s Isabella Stewart Gardner Museum in March 1990.

Gentile has repeatedly denied knowing the whereabouts of any of the art, valued at an estimated $500 million.

At a 2015 hearing, prosecutors said Gentile was secretly recorded telling an undercover FBI agent that he had access to at least two of the paintings and could sell them for $500,000 each. Gentile denies knowing where the artwork in.

At Tuesday’s hearing, a federal judge rejected Gentile’s plea that he be sentenced to the nearly three years he has already spent in custody since his April 2015 arrest. Read more