Boston Globe: Photo by Steven Senne/AP at FBI conference

The FBI and the Isabella Stewart Gardner Museum ­received a flood of tips from around the country Tuesday, as new details emerged about the turning point in the investigation of the notorious Gardner Museum heist 23 years ago. 

The latest, exhaustive phase in the inquiry is based on a tip that a caller made to authorities in 2010, according to Anthony Amore, the Gardner Museum’s head of security and chief investigator. 

He said Tuesday that the tip was so fruitful — leading to the announcement that investigators know the identities of the thieves and could trace the art from Boston to Connecticut and Philadelphia — that the FBI has since rededicated significant resources to investigating the heist. 

“That tip, plus thousands of man-hours, led to where we are today,” Amore said.

The latest focus has been on Robert Gentile, a 75-year-old ailing Mafia figure with ties to organized crime in Philadelphia and Boston. His Connecticut home was searched last year in relation to the heist. He was charged with drug dealing and possession of an illegal firearm in what his lawyer called a tactic by the FBI to pressure him to disclose information about the heist. 

Gentile, who pleaded guilty and is slated to be sentenced in May, faces a lengthy prison term. His lawyer, Ryan McGuigan, has maintained that Gentile knows nothing about the heist or the whereabouts of the artwork. 

But investigators seem to have trained their focus on Gentile in the recent phase of the investigation. 

A person with knowledge of the FBI investigation, who asked to remain anonymous ­because of the sensitivity of the inquiry, confirmed Tuesday that investigators found a list of the art stolen from the Gardner, and the estimated value of the works, during the search of Gentile’s home. The discovery of the list was first ­reported by The Hartford ­Courant. 

Gentile also had close ties to organized crime figures in Philadelphia and in Boston, including the late Robert Guarente, who has been tied to almost every­one mentioned as a person of interest in the heist. 

Guarente, for instance, was close with the late Carmello Merlino, who ran an auto body shop in Dorchester and who, according to FBI reports, once tried to negotiate the return of the artworks. No deal ever came to fruition, and Merlino was later convicted in a scheme to rob an armored car depot in Easton. He said that he was set up by informants and that the FBI was pressuring him for ­information regarding the Gardner heist. Merlino died in prison in 2005 at age 71. 

Two other men were also convicted in the armored car depot scheme and received lengthy prison sentences, though they have denied knowledge of the heist or the ­location of the artwork. ­Stephen Rossetti, 54, who is Guarente’s nephew, is slated to be released in 2044, and David Turner, 45, is set to be released in 2025. 

Guarente died in 2004 at age 65. His wife has told authorities in recent years that she saw him give Gentile at least one painting some time around 2003, around the time authorities say some of the art was offered for sale in Philadelphia. The wife, however, did not describe the painting as one of the works taken from the Gardner.

In a stunning development in the investigation of the world's richest art heist, law enforcement officials said Monday they know who stole $500 million in master works from Boston's Isabella Stewart Gardner Museum and disclosed new detail about their interest in Hartford mobster Robert Gentile.

"The FBI believes with a high degree of confidence in the years after the theft the art was transported to connecticut and the Philadelphia region and some of the art was taken to Philadelphia where it was offered for sale by those responsible for the theft," said Richard DesLauriers, Special Agent in Charge of the FBI's Boston office. "With that same confidence we have identified the thieves who are members of a criminal organization with a base in the mid-Atlantic states and New England."

But since 2010, Gentile has been questioned repeatedly about his membership in the Boston branch of a Philadelphia-based criminal organization, as well as leads that place at least some of the stolen paintings in Connecticut and the Philadelphia area.