A stolen Roy Lichtenstein painting, missing for 42 years and now worth $4 million, was returned Tuesday to a New York widow whose art dealer husband purchased the piece in the 1960s for $750.

The piece disappeared after Greenwich Village art dealer Leo Castelli sent it out for cleaning in 1971 and apparently lost track of it, his widow said Tuesday.

"He remembered it and didn't know where it had gone," Barbara Castelli said at a news conference during which federal prosecutors and FBI agents returned the artwork to her.

She said she plans to hang the piece in her home.

Leo Castelli hosted Lichtenstein's first solo show in 1962, according to his gallery, and later purchased "Electric Cord," which depicts a tightly wound cord in black paint on an off-white canvas.

Federal officials said Castelli sent the piece to art restorer Daniel Goldreyer in January 1971 and an employee apparently stashed the painting in his work locker. It remained there until 2009 when Goldreyer died, U.S. Attorney Preet Bharara said.

Goldreyer's widow, Sally, told federal investigators that the employee asked her to sell the painting for him. Not knowing it was stolen, she agreed to sell it to an art gallery in Colombia.

In June, a buyer contacted the Roy Lichtenstein Foundation and asked for assistance authenticating the work, which the buyer said was stored in a New York warehouse. The foundation contacted Castelli, who called authorities.

Bharara declined to comment on discussions with Goldreyer, but said his office had been "prepared to take real action" against her, a sentiment echoed Tuesday by the FBI.

"Even when there is no crime charged, the FBI's expertise can be valuable in ensuring that works of art end up with their rightful owners," said Belle Chen, acting director of the criminal division at the FBI's New York field office.

The FBI's Art Crime Team maintains a list of its top 10 art crimes, similar to the bureau's Most Wanted List, said Jim Wynne, a New York FBI agent who specializes in art theft.

Among the current top 10 art crimes under investigation are a $30 million theft from Amsterdam's Vincent Van Gogh museum in 2002 and the theft from a Houston home in 2011 of a piece by French painter Pierre Auguste Renoir.