Los Angeles — The FBI is asking for the public's help to find two of six valuable N.C. Wyeth paintings nabbed from a home in Maine in 2013.

The agency announced Tuesday that it's now offering a $20,000 reward for information leading to the two stolen paintings. The four other stolen Wyeth paintings were recovered from a Beverly Hills, California, pawn shop in December and are estimated to be worth up to $2 million.

Three men have been convicted in connection with the stolen paintings, but FBI Special Agent Elizabeth Rivas says the person responsible for taking them remains a mystery.

David Bowdich, assistant director in charge of the FBI's Los Angeles field office, says the remaining paintings could be anywhere in the world and like other stolen art, could take decades to find.