The FBI offered a reward of as much as $20,000 on Tuesday for help finding the last two of six valuable paintings by the New England artist N.C. Wyeth that were stolen from a private art collector in Portland, Maine, in 2013.
Federal agents recovered the four other stolen paintings from a luxury Beverly Hills pawnshop in December after the works were driven to Southern California in an effort to find a buyer, authorities said.
Investigators believe the remaining paintings -- "The Encounter on Freshwater Cliff" and "Go Dutton, and that Right Speedily" -- are still somewhere in New England, authorities said.
Three men -- Lawrence Estrella, Dean Coroniti and Oscar Leroy Roberts -- have been convicted for their roles in transporting and possessing the stolen artwork, authorities said.
David Bowdich, assistant director in charge of the FBI's L.A. office, said the men operated with "some level of sophistication."
"There is some merit to the fact that they removed the paintings from the north New England area where it was too hot to sell ... and they came to an area with a lot of people and a lot of money," Bowdich said.
Wyeth was a renowned American realist painter and illustrator from New England who died in 1945. His son, the painter Andrew Wyeth, died in 2009.
The four recovered paintings have been appraised at as much as $2 million, Bowdich said.
Estrella, 65, of Massachusetts, pleaded guilty to interstate transportation of stolen property this year and was sentenced to 92 months in prison for driving the four paintings nearly 3,500 miles across the country in a green Mercedes, according to court records and federal authorities.
Coroniti, 55, of North Hollywood, pleaded guilty to possession of stolen property for his role in storing the paintings and will be sentenced in October, according to the FBI.
Roberts, 37, also of North Hollywood, pleaded guilty to transporting stolen property and lying to federal agents about the location of the paintings. He was sentenced to 28 months in federal prison, according to federal authorities.
Authorities said Roberts, an aspiring rapper who boasted about his celebrity connections, used the paintings to secure a $100,000 loan from the Dina Collection, the Beverly Hills pawnshop featured on the cable reality TV series "Beverly Hills Pawn."
Beverly Hills Police Chief Dominick Rivetti said a city detective became suspicious of the origins of the paintings as she was reviewing pawnshop slips last year. The detective, Michele Fieler, searched Google and the FBI's stolen artwork database and discovered the paintings had been stolen.
"The investigation into the theft has been an active and aggressive effort, with law enforcement following leads and tracking down potential sources of information across the country," said Vincent B. Lisi, special agent in charge of the FBI's Boston Division. "I'm optimistic that one day soon the paintings will be returned to their rightful owner and we'll bring those responsible to justice."
Anyone with information should call the FBI at 1-800-CALLFBI (1-800-225-5324). Tips may also be submitted online at https://tips.fbi.gov.